Ranma, the only son of Genma and Nodoka Saotome, was taken from his home by his father when approximately 2 years old, to begin a 13-14-year training trip to perfect his skills in the martial arts.
While he was still a child, he befriended Ukyo Kuonji, the daughter of a travelling okonomiyaki chef and martial artist, although he was unaware that she was a girl. Genma engaged Ranma to Ukyo in exchange for her father's food cart, but he abandoned Ukyo and ran off with the cart without ever telling Ranma about the engagement or correcting him about Ukyo's real gender.
Later, near the end of the trip, Genma took Ranma to a training ground in China named Jusenkyo that few people used, due to the springs being cursed. Falling into them would transform a person into whatever first fell in. Not knowing this, and not having the patience to listen to a warning from the local guide, Genma attempted to train with Ranma atop the bamboo poles which jutted up out of the pools. When Ranma knocked Genma into Shonmaoniichuan/"Spring of 'Drowned' Panda", he was surprised to watch a panda emerge from the pond and leap onto one of the poles. Genma, now cursed, was able to hit a surprised Ranma into Nyannichuan (Niángníquán 娘溺泉), or the "Spring of 'Drowned' Girl". Thus he turns into a female version of his original form when splashed with cold water, which is only (temporarily) reversible through contact with hot water.
Before this incident, Genma had made an arrangement with his best friend Soun Tendo that Ranma would marry one of Soun's daughters and carry on the Tendo Dojo. After learning of Ranma's condition, Soun's daughters Kasumi and Nabiki began to insist that Ranma choose their younger sister Akane, and rationalised that a tomboy would be a more appropriate fiancee for a man who transforms into a woman. Although Akane and Ranma were initially unwilling to be engaged, they develop feelings for each other, while generally struggling to deny or otherwise avoid openly expressing throughout the entire series.
Ranma and Genma moved in as houseguests of the Tendo dojo. Since then, Ranma has endured, among other things, Amazons, old rivals, Dojo destroyers, and even evil demons. Female Ranma has also received a few male suitors, such as Tatewaki Kuno and Mikado Sanzenin.
After receiving a letter from his wife, Genma revealed that he had promised that Ranma would return "a man among men", and that if he failed, they would commit seppuku, a suicidal ritual. Therefore, in order to meet his mother without dying, Ranma changed into a girl during her visit, and presented himself as "Akane's cousin Ranko," accompanied by her pet, "Mr. Panda."
Ranma made several attempts to talk to his mother without revealing his curse, to prove his manliness, but was generally stopped by Genma, and after being caught cross-dressing, he had to pretend to peek on Akane taking a shower to show his manliness. Eventually, after he saved her life, Nodoka accepted Ranma as a boy despite the curse.
Rumiko Takahashi herself has described Ranma's personality as a mixture of nice, clean-cut, frank, energetic, indecisive, stubborn, picky, stingy and sly, and has stated that she finds flawless characters rather boring.
She addressed the origins of the character as: "With Ranma ½, I had thought a lot of doing a series with a male/female like protagonist, and since in the greater part of my previous stories the main character had been a woman, I planned to use a man this time. I was worried about writing a male main character because of the hundreds and hundreds of male readers, therefore I decided on the character being half man and half woman."
Under normal circumstances, Ranma is fairly carefree and generally friendly to those around him. He has stated on various occasions that he sees it as a martial artists' duty to protect normal people from monsters, the supernatural and similar threats, and has saved bystanders in danger of getting hurt. A perspective he apparently shares with several other Japanese martial artist cast members. However, he also lacks experience in social situations and frequently speaks and acts without considering the consequences, or the feelings of others.
He sometimes insults people by bluntly gloating about inflated perceptions of his prowess, or taunting them about their perceived flaws. For instance, he once boasted that his female form had a larger bust than Akane, despite that she was happy about her own growing bosom. Early in the manga, he borrowed Akane's overalls while his own clothes were in the laundry and casually mentioned that the waist area had plenty of room and was tight at the bust. He frequently insults the areas his fiancée has complexes about, by calling her an over-muscled, overweight, un-cute, clumsy, macho jock tomboy with poisonous cooking skills. Ranma has also given other people insulting nicknames, with shifting degrees of justification, for example calling Cologne "old hag" or "old ghoul", Happosai "old freak" or "old letch", Ryoga "clueless moron" or "sucker", Nabiki "heartless bitch", or Taro "pantyhose guy", but this is also a rather frequent trait among other characters.
Ranma apparently has little respect for authority figures, such as his father, his teacher Hinako Ninomiya, or Principal Kuno. His willingness to fight back against the latter seems to have gained him some respect from his schoolmates, but they have also stated a certain contempt due to his shamelessness and weird condition. He is quite irresponsible and almost completely uninterested in academics. Ranma often skips school, flaunts its regulations, and otherwise dodges situations that don't involve martial arts or his personal interests. Other examples include juggling his various paramours and fighting tooth and nail against Hinako's attempts to give him private tutoring in English, though the two of them mutually respect each other's determination in their respective, albeit contradicting, endeavors. He also has a habit of interfering with certain situations that are generally none of his business (this happens twice as much in the anime then it does in the Manga).
It is relatively easy to embarrass him. When faced with such a situation, he can freeze up or verbally lash out when found in highly incriminating 'amorous' positions. Nabiki has sometimes taken advantage of Ranma's lack of finesse and weak defenses against crying or emotional girls, manipulating him and various situations to her own advantage.
He takes great pride in his prowess as a martial artist and occasionally brags about it. Although he frequently has the skills to back it up, his overconfidence can also lead to trouble. Ranma tends to rely on blunt tactics and planning, but he is adept at learning from his mistakes in a fight and generally takes advantage of an opponent's weaknesses during a later encounter. He will not back down from a challenge during very serious situations, or when his pride has been wounded, even if he is completely outmatched and unsure of how to overcome an opponent. Despite this, he will apparently refuse a match if he considers the opponent to be too ridiculous, given that female Ranma tried to withdraw when set up to fight the monkey Sanae in "martial arts tea ceremony".
His pride recurrently results in him being unable to accept defeat, and becoming preoccupied with trying to win the next skirmish against his foe. He also has a prominent petty side to his character which manifests itself in these situations. If he's repeatedly defeated, humbled or otherwise feels humiliated, he takes it personally, howling statements of revenge at the moon or even crying on the floor. He will frequently stoop to trickery or cheating in the rematch. Among many examples, he couldn't stand seeing Akane become more powerful through the use of super-strength soba. Nabiki and Kasumi both observed that he held a big grudge after she turned back to normal, which he satisfied through gloating while repeatedly defeating her in arm-wrestling. He was also willing to 'feign' love for her strictly to get rid of a similarly enhancing sentient battle-dougi, since he couldn't stand the thought of her being more skilled than him, but apparently also partially because it was a severe nuisance and kept coming between them.
Ranma is quick to use insults and / or violence when dealing with those who upset him, typically worsening the problem instead of solving it. Using diplomacy, money, or blackmail seems too complicated, or in the last case, dishonourable for his tastes. Although he sometimes uses his sexy female form, in conjunction with a fabricated innocent persona, to convince hormonal boys to treat him / her to food, or buy something he is attempting to sell, alternately to frequently set up simple schemes to fool, make fun of, or play with Ryoga's feelings. Ranma says he doesn't like fighting women, but he has fought them (and a few he's mistaken for women such as Tsubasa and Konatsu) on numerous occasions in both his male and female forms, but has stated that he's held back in a few of them, though he seemed to have no problem holding back trying to harm (or even kill) Kiima during the Phionex Mountain Saga.
While he occasionally blames others for his problems, Ranma has sporadically taken responsibility for matters not mainly his fault, such as when Akane's hair was accidentally chopped off during his first fight with Ryoga, or trying to soothe Ukyo's rage at being left behind.
He has protected all of his fiancees at different times, with one of the best examples being when he saved Akane from the hungry Yamata no Orochi, although she returned the favour, and has saved or helped him a comparable number of times. He's even rescued enemies, such as Herb, who was trying to kill him. Ranma has a low tolerance for people who try to steal from him, manipulate him, or otherwise treat him very badly, such as Nabiki or Happosai. He generally considers Tatewaki, Shampoo and Kodachi to be annoying pests.
He can also be very forgiving and usually doesn't seem to stay mad for very long. For instance, despite that Herb severely tormented him out of sheer malevolence, he still opted to save the latter's life. Ranma has also made efforts to help out Tatewaki or Mousse, and refrained from seeking revenge against the Phoenix people after his conflict with Saffron. While his father frequently stole his food when he was small, and subjected him to the Cat-Fist technique, he usually just seems mildly irritated. Although he has also been vengeful at times, repeatedly beating up Genma upon learning that he had become superior to his father in general hand-to-hand sparring. He has reacted in a similarly harsh manner whenever the latter interfered with the reunion of Ranma and his mother.
Another exception to this rule would be Happosai, whom Ranma has been stated to truly hate, and apparently considers a personal archenemy according to The art of Ranma½ relationship chart. He never misses an opportunity to trick or torment the ancient pervert, and once explicitly attempted to kill the grandmaster by punting him and a 5 m diameter Happo Fire Burst over a cliff (though it was shown later in both versions of the story that Happosai survived and later in the anime version blew the gender-bender up with a another Happo-Fire Burst), even before he almost turned Ranma powerless for life thanks to a weakness moxibustion point, although that may simply have been for comic relief. Even Happosai, however, has been a recipient of Ranma's compassion. Most notably, Ranma permitted him to come back to stay at the Tendo Dojo after finding him marauding a tourist resort disguised as an octopus jar (for thievery and peeping in the manga, and to help a starving young girl named Tsukasa in the anime), when the latter became very sad from loneliness. He also helped to save the sprightly senior's life by eventually deciding to assist in creating a rejuvenation potion, and together with Akane freed him from a death curse cast by a matronly ghost.
One of Ranma's worst habits is that when preoccupied with his own thoughts or training with his father, he is generally oblivious and unmindful about his surroundings. The most notable consequence of this is when female Ranma accidentally kicked Ryoga into the "Spring of the Drowned Piglet" while pursuing his father at the cursed springs of Jusenkyo, effectively ruining the latter's life even further than previously. He's accidentally mowed down child Hinako when late for school, but Tatewaki's head is his most frequent "stepping stone," which appears to be intentional since the two despise each other. Another victim of his carelessness is the Frog Hermit, who was knocked into the "Spring of the Drowned Frog" when Ranma accidentally kicked out his bamboo pole from under him (this only occured in the anime).
Ranma has often professed his wish to become all male again. However this has not stopped him from using his girl identity to his advantage. He has often used his female form to conceal his true identity from others, most notably Ryoga, and his mother, Nodoka. Other times he has used it to obtain favours from Tatewaki, or other situations when being female would benefit him. Sometimes, he's even taken pride in that his girl form is more attractive than Akane. In the anime, he enjoys ice cream Parfait, although he is always female when she eats them because he considers it somewhat embarrassing for men to consume.
Ranma's speech is casual and unrefined, using a coarse form of Japanese (English in the case of the American-translated anime and manga). He rarely uses -san, -kun, -chan or any other traditional Japanese honorifics. He does use -sempai (elder student) for Kuno, but that is more for sarcasm. Others he uses honorifics for include his benefactor Soun (Ojisan or "Uncle"), his childhood friend Ukyo (Ucchan), the considerate Kasumi (usually -san), and even Ojiisan and Obaasan for Happosai and Cologne when he's not mad at them. And while Akane usually uses honorifics for other people, she rarely addresses him with one. This is amusing since it would denote that the two are particularly intimate with each other.
Although Ranma turns into an attractive girl, he has a very strong heterosexual male gender identity, such that even while female himself, he still feels uncomfortable in the presence of naked women. His masculinity is so strong that he prefers to wear boxer shorts under his clothes even when he dons feminine garments such as dresses. During the moxibustion story arc, however, he learned how to use the emotion dampening aspect of his Soul of Ice training to suppress his pride and posed for pictures in lingerie as part an effort to defeat Happosai, and later did the same to appease Nabiki when accidentally destroying her concert tickets. Men who try to get grabby (even accidentally), such as Tatewaki or Happosai--who especially disgusts him--generally get pummelled.
But since Ranma is a man, he has little feminine modesty. He sometimes removes his shirt in public, as he is generally unaware of the effect that the sight of his unclothed female body has on others. The guys at school appreciate this side of Ranma as it offers them a free glimpse of his exposed chest, and they openly wish there were more girls like him. His worst nightmare is being kissed by a man, and he even has two hideous dreams: one in which he was a girl and married Tatewaki, spawning several children and in the first season when he had a dream about Tatewaki asking him to marry him in both forms. Ranma does however receive his first kiss, excluding Shampoo's kiss of death, while a female from Mikado Sanzenin of the Golden Pair of Martial Arts Skating, an occurrence that, by Ranma's own admission, made him truly angry for the first time.
A running gag through the series is that Ranma is sometimes accused of doing perverted things but rarely actually committed the accused act. During P-Chan's (Ryoga's cursed form) first appearance, Ranma tried to threaten him to get out of Akane's room, but was manoevred into falling on top of Akane's sleeping body. In an attempt to find the Japanese 'Spring of drowned man' he also disguised himself to gain entrance to the girls' locker room while they were still changing clothes, and accidentally tipped Happosai's stash of stolen underwear over himself in front of his classmates. Other examples include when Shampoo has turned up naked and hugged him in the Tendo bath, crept into his bed without his knowledge or when they both ended up in the Kuno bathtub. Usually right before Akane sees him through the open doorway. Another double misunderstanding happened when Kodachi once doctored a photograph to show them kissing, and Ranma tried to get the negative from Tatewaki by offerring to bathe with him.
In reality, however, he's a bit prudish, though not close to Ryoga's level. The concept of kissing Akane, even as part of a school play, is enough to fluster him. So was simply receiving a heartfelt hug from her because he survived the battle against Herb. His defences have occasionally been shaken, for example, when Kiima or a spirit doll assumed Akane's form and made sexual advances toward him, or when Akane hid with him in a closet, and he mistakenly believed that she wanted sex. Also notable is when Nabiki assumed a cute face and declared her deep love for him (actually just sadistic play-acting), and Shampoo's soothing and cuddling him during her first appearance. But beyond these few exceptions, Ranma's reaction to such situations is generally one of fear and confusion, possibly because any admission of love on his part will force him into a wedding for which he is not yet emotionally prepared.
Fighting Style: Trained from the time he was very young by his father in the ways of the Saotome family's style of Musabetsu Kakutō Ryū kenpo ("School of Indiscriminate Grappling," more commonly known in the West as "Anything Goes Martial Arts"), Ranma is a master of several styles of martial arts, utilizing a blend of Chinese and Japanese techniques. The other branch of Anything Goes, the Tendo School, is practiced by Sōun and Akane. Ranma is seen as the school's primary heir.
A practitioner of the Anything Goes Martial Arts is expected to be prepared to do almost anything to triumph, regardless of the challenges, humiliations, or cheating involved. This versatile combat style can produce a warrior who is strong in virtually every aspect of battle, both mentally and physically, with limited weaknesses. In most fights, neither form has a discernible advantage, as they both perform equally well. Ranma is, however, stronger with a longer reach in his male form, and faster and more agile as a female. His training has made him a very balanced fighter, though he can still be surprised by opponents whom he has never fought before.
His impressive physical abilities include incredible strength, and outstanding speed. He also has superhuman endurance, enabling him to continue fighting even after he has taken many powerful blows or fallen from a great height.
Swiftness: As a gauge of the extent of Ranma's speed, he has been able to land 518 blows during a very brief ice-skating skirmish with Mikado Sanzenin, even before undergoing Cologne's speed training. Afterwards, he was referred as able to land "a few hundred punches" on Ryoga so swiftly that it looked like a single strike, or shown to catch over a hundred pebbles from the latter's Bakusai Tenketsu rock explosion within at most a few seconds. If the above gauges are accurate this would make him able to move at supersonic speeds, but apparently only uses it in combat situations, and was stated as greatly exerted from intensive prolonged usage.
Stamina: He's durable enough to withstand the full power of Ryu Kumon's, large, stone Buddha-statue splitting, "demon god assault bomb" vacuum blade-barrage, and immediately continue to fight afterwards, (which, at the very least, would qualify him as bulletproof), managed to withstand exposure to Rouge's and Saffron's firestorms, and has fallen hundreds of meters into solid stone with only minor bruisings. Regarding his limits, when in a state of surprise, a single strike from Taro in his cursed form almost rendered female Ranma unconscious after crashing into a stone palisade. Although later, during their aerial battle against Rouge, he was only momentarily stunned.
Ryoga's regular Shi-shi Hokodan (a technique used to clear out cave-ins, or to help blow tunnels through the earth) has knocked him out in one blow, or required a few to several shots, depending on the latter's focus. This version even managed to stun Ranma for a few seconds when Ryoga was turned into a small child.
Even being partially hit by the outermost limit of the perfect version was enough to instantly knock him out, despite attempting to lessen the impact with his weakened Moko Takabisha. Although a later, attempt, during the their fight, only stunned him for a minute at most (note: no change was noticeable in the size of the crater at this point), and he was able to handle them much better by distracting Ryoga into absorbing most of the impact. At the end of the fight he synchronised his movement with a falling, even more powerful, "ultimate" version, defeated Ryoga by merging the impact with a surprise blow to his head, and remained conscious long enough to declare victory.
Happosai's smaller Happo-daikarin are also shown as capable of downing him in one strike, which is understandable, given that they have proved able to repeatedly do the same to Taro's considerably more durable cursed 'monster' form, but he's withstood them on other occasions, so it apparently depends on the force his grandmaster puts into them.
Strength: Ranma's physical power seems to be portrayed somewhat inconsistently depending on story convenience. He broke his legs from the impact of a 50-100 metre fall while carrying four girls, but was likely still severely weakened from poison at the time, so his peak effort should be multiplied. Male Ranma proved unable to get out when stuck under an 90-100 tonne large iron bell, but wasn't significantly motivated and had no grip. Female Ranma almost effortlessly pushed a roughly 40-tonne boulder into the mouth of the Yamata-Orochi while swimming underwater, when supremely determined to save Akane from being eaten, and also managed to support the pressure Ryoga exerted on two enormous floating slabs of ice, one of which had an approximate weight of roughly 206 to 642 metric tons, when the latter was standing on her head. Thus, he would presumably have succeeded with better leverage and motivation.
Given his ability to contend with Ryoga, who by all appearances could exert force equivalent to lifting at least several thousand tonnes under optimal circumstances, he must be at least a tenth as strong himself, and very likely considerably higher. Although comparatively weaker, Ranma seems to have superior conscious control of his abilities, and can more easily dial it back during basic social interactions, while Ryoga occasionally breaks anything he touches. That said, he has stated outright that he generally honours his opponents' pride by fighting full force, and refuses to give up both for himself and because he thinks a hollow victory would never be satisfying in a battle between honourable men. More notedly in battles with Mousse and Gosunkugi, but he has also occasionally restrained himself, as in battles with Akane, Shampoo, or (initially) Ukyo and Konatsu.
Striking Force: As a gauge of female Ranma's hitting power, a few moments of focusing her energies proved sufficient to split a 3m-3.5m diameter boulder with a single strike, while male Ranma managed to immediately shatter a 2m-2.5m version.
Attitude to combat: As noted previously Ranma has stated that he tends to fight upfront at full force against male opponents, as he considers any less as an insult to his opponent's pride as a fighter, but also that he "always takes advantage of an opponent's weak spots", and recurrently uses trickery, severe distractions or sucker-punch combinations if he cannot win through other means, or if it is most expedient for handling situation as quickly as possible. He generally seems to trust in his own power, but under extreme circumstances he is willing to use multiple crutches if he thinks the opponent does as well.
However, he has also stated that he hates fighting women, and initially greatly held back against Konatsu because of this reason. He has likevise explicitly tried to strictly tie up, or othervise incapacitate without harming Akane, and Shampoo, but has apparently at least been willing to render Rouge, and Kiima, unconscious. His overconfidence has been taken advantage of by Cologne by holding back her true power, allowing Ranma to believe that he had the edge, and tricking him into accepting a bet to marry Shampoo if he lost. He has also been manoeuvred into inefficient fighting by an opponent even more prone to cheating than himself, as Taro managed to goad him into repeated sucker-punch attacks, in an area filled with water-traps.
Ranma has repeatedly been unable or unwilling to accept defeat, regardless of how outmatched he is, or how irrational this may turn his behaviour, although his confidence can be shaken enough to not be able to use the Moko Takabisha. He recurrently brags about his inflated sense of prowess, arrogant in the face of hurt feelings or possible payback. However, with the possible exceptions of Happosai, or Ryoga and Akane (while not remotely himself due to magical brainwashing), he has apparently avoided consciously attempting to kill his opponents, and even saved the vicious Herb from being crushed under a crumbling mountain. Although, when given no apparent alternate solution he did deliberately take this step against Saffron in the final storyline.
Ranma has proported himself as able to win any competition in which martial arts are involved, and as the story progresses, he learns to use several outrageous or virtually useless styles, such as Martial Arts Figure Skating, even though he initially couldn't skate, Martial Arts Tea Ceremony, Martial Arts Dining, and Martial Arts Cheerleading, although he's never been seen to use them outside of the original environment.