Akuma is the Japanese word for devil.
In the original Street Fighter II the Japanese to English translation for Ryu's victory speech was supposed to be "You must defeat my dragon punch to stand a chance", but was translated incorrectly as "You must defeat Sheng long to stand a chance".
This sparked many rumors about whom Sheng Long was? Fan fiction created a world wide rumor that Sheng Long was the master instructor of Ryu and Ken. Capcom ceased the moment and created a new secret boss for SSFII Turbo , but named him Akuma, or Gouki in Japan.
The character was invented as a new secret boss for this game to satisfy the urge of fans wanting Sheng Long.
Later Capcom began a story line where Shen Long is in fact the teacher of Ryu and Ken and his mortal enemy is Akuma/Gouki, who depending on the incarnation of the story, is either Shen Longs brother, ex-best friend or a rouge student.
The street fighter Akuma (also known as Gouki in Japan, Asia, South America and Australia) makes his debut in this 4th edition to Street Fighter II: The World Warrior [1991] as a hidden boss and a secret character to this game.
Akuma (a.k.a. Gouki) replaced the three bonus stages from the previous Street Fighter II versions.
Akuma (a.k.a. Gouki) is an unofficial contestant in the Street Tournament II like how Ken Masters is an unofficial contestant in the first Street Tournament.