Bowser is the main villain of the Mario series, and king of the Koopas. When first introduced in Mario 1, he was refered to as 'King Koopa'. This changed with the release of Super Mario World in 1990.
In Contest terms, Bowser is a bit of an oddball. When given an opponent the Nintendo fanbase can rally against he can do some pretty impressive things, such as holding Snake to under 51% in 2005, keeping Sephiroth under 60% in the Villains Contest, and putting up almost 59% in a direct matchup with Ryu. But give him someone the Nintendo fanbase will support and he quickly falls apart, as in his awful SFF loss to Mario (2004) and his embarrassing showing in the 2007 Contest, where drainage from Mewtwo and Toad left him with so few hardcore supporters that Ryu was to turn the tables and easily advance ahead of him. Though not even LFF can explain why Ryu again owned him when Mewtwo and Toad were replaced with Auron and Shadow.