Akuma isn't one of the original Street Fighters. He made his first debut in Super Street Fighter II Turbo, the fourth version of Street Fighter II. Though, you might not have seen him unless you were an especially proficient player or had access to cheats. Akuma began as a secret character. Rather than only remaining hidden for one game, he's remained a secret through many installments in the series. If you wanted Akuma, you almost always had to work for him.
Now THIS article right here is a true gaming article granted many old schoolers like myself know this but, its informing the others that didnt live those games or generations.
Akuma and Ganondorf seem to be shopping at the same hair salon these days
Really loving him so far in SF5, his new design isn't great but his moves and combos are awesome.