Street Fighter II invented the competitive fighting game genre as it exists today: six attack buttons, a roster of distinct characters with unique move sets, frame data that rewards mastery, and a competitive ecosystem that has persisted for three decades.
Follows: Street Fighter
Before Street Fighter II there was no "fighting game genre" in the sense that exists now. There were beat-em-ups (Final Fight, Double Dragon), one-on-one combat games (Karate Champ), and the original Street Fighter — none of which had the combination of character diversity, input depth, and competitive symmetry that SF2 introduced. The game's release in 1991 triggered an immediate wave of imitators: Mortal Kombat (1992), Virtua Fighter (1993), Killer Instinct (1994), Tekken (1994).
Every one of those games was a response to Street Fighter II. The genre it created has supported professional competition at the highest level for thirty years. EVO, the Evolution Championship Series, began in 1996 as a Street Fighter II tournament and has grown into the largest fighting game event in the world. The game's influence is not historical — it is present and ongoing.