Short answers, pulled from the story.
Akuma first appeared in the arcade version of Super Street Fighter II Turbo on the 1st of March 1994. He emerged as a secret boss who could only be unlocked by meeting specific, obscure conditions.
Designer Akiman created the character Akuma in a single hour. The design was influenced by Kongorikishi statues and instructed to be similar to the Super Saiyan transformation from the Dragon Ball franchise.
Akuma is the younger brother of Gouken, the master of Ryu and Ken. Their shared history involves a fatal confrontation where Akuma defeated his brother after embracing the Satsui no Hadou while Gouken sought to master it to protect the world.
Akuma appears as a guest character in Namco's Tekken 7. In this game, he seeks to repay a debt to Kazumi Mishima for saving his life from an unknown critical situation.
WWE wrestler Roman Reigns entered negotiations to portray Akuma in the upcoming live-action Street Fighter film co-produced by Legendary Entertainment and Capcom. He had officially been cast in the role by July.
The Raging Demon is Akuma's signature move where he grabs his opponent and the screen goes black. Prima Games named it the seventh-greatest fighting move in video game history.