Akuma is the secret boss character in Super Street Fighter II Turbo. Known as Gouki in Japan, he appears as a hidden opponent when the player meets specific performance requirements during arcade play.
In the game's dramatic boss sequence, Akuma interrupts the expected final confrontation with M. Bison, defeats Bison, and challenges the player instead. This made Akuma different from a standard selectable fighter: he was a hidden character, an alternative boss, and one of the most powerful combatants in the game.
Akuma's debut in Super Turbo also established his central story role. He is Gouken's younger brother and pursues the lethal power known as the Satsui no Hado, placing him in thematic opposition to Ryu and Ken's more disciplined martial-arts path. The character later became a regular presence across the Street Fighter series.
A common mix-up is calling him Shin Akuma; that is a stronger variation introduced in later games and versions, not the original secret boss identity in Super Turbo.