Short answers, pulled from the story.
Street Fighter III is a 1997 fighting game in Capcom's Street Fighter series, originally released as a coin-operated arcade game. It is the sequel to Street Fighter II from 1991 and introduced an all-new roster led by a character named Alex.
Street Fighter III first reached arcades in 1997, after Capcom announced it was in development on the 27th of March 1996. It was followed by two updates, 2nd Impact in 1997 and 3rd Strike in 1999.
Gill is the final boss in Street Fighter III, taking over the role M. Bison held in earlier games. He leads a secret organization that wants to turn the Earth into a utopia and can manipulate fire and ice.
Capcom kept Street Fighter III in 2D because general producer Noritaka Funamizu felt 3D was not suitable for head-to-head fighting games and that Capcom lacked the technique for high quality 3D graphics. The company's 3D ambitions went instead into a separate spin-off game, Street Fighter EX.
Street Fighter III introduced parrying, which lets a player deflect an incoming attack without taking damage by moving the controller toward or down at the exact instant it would land. It also introduced Super Arts, powerful character-specific special moves chosen before a match.
Street Fighter III received a mainly positive reception but did not become as big a hit as its predecessor. In Japan it struggled to break even despite a budget of 1 billion yen, roughly $8 million, selling only 1,000 cabinets there.