Bowser, also known as King Koopa, in Japan, he is called Koopa (クッパ Kuppa?). Bowser is said to be "King of the Koopas," the race of sinister turtle-like creatures that co-exist with the Mushroom people that inhabit the Mario universe. In many games, particularly the RPG series, Bowser is presented as being considerably more villainous than the other members of his "koopa troop," who are mostly just followers, flunkies, or admirers of his strength or personality.
Bowser is perhaps most famous for his repeated kidnappings of Princess Peach. The reason for these kidnappings has changed dramatically over the years, from the fact the Princess is the only one who can undo Bowser's black magic, to the fact he has some love and devotion towards her. All the same, he can use her in his plans to take over the Mushroom Kingdom.
Bowser's appearance has been tweaked several times throughout the series, but most of basic overall look has been consistent. Despite his name, he actually looks something like a cross between a Koopa Troopa and a dragon, although he is associated more with fire instead of water. He is bipedal, with large claws on his hands and feet. He is noticeably larger than all the other characters ( in the upcoming TV episodes and video games, he will be replaced by Daxian as the largest character in the series). He is mostly orange with a green shell. Several large spikes are located both on his tail and on his shell. His alligator-like jaw and stomach front are yellowish-beige. He sports a mane of fiery red hair on top of his head with a horn on either side. He also wears spiked metal cuffs around his wrists, biceps, and neck. Although his abilities vary from game to game, he is able to breathe fire in most of them.
Bowser's abilities greatly vary from game to game. His most common physical traits are the ability to breath fire, and being extremely durable. He is in fact generally immune to standard attacks. His mobility greatly varies. In games where Bowser is playable, he's always depicted as extremely slow. When he's an enemy, he's even faster and more agile than Mario. Outside his common abilities, some individual games generally give attacks that aren't seen in others, such as being able to create shockwaves or flaming boomerangs. Nearly every game also shows him wielding immense physical strength at some point.