Retsu

Retsu (烈, lit. "Furious") is a non-playable character from the Street Fighter series who first appeared in the original Street Fighter game as one of the ten computer-controlled opponents. He is a master of Shorinji Kempo who fought in the first world warrior tournament. While the character never appeared in another Street Fighter game, he still forms part of the later games' backstories (being established as a friend of Ryu and Ken's teacher, Gouken).

Story
Just before the first World Warrior tournament, Retsu was indefinitely suspended from his temple for using forbidden techniques.

Street Fighter
Retsu loses to Ryu in the first world warrior tournament in front of a temple in Japan.

UDON comics
Retsu appears in the UDON comic series of Street Fighter, where he is an assistant of Goutetsu at his dojo; he is first seen making food for an injured Akuma.

Retsu paid a visit to Gouken in the mountains, informing him that Goutetsu was the only other student who was able to stay in the mountains for fourteen days without food and water, informing him that he has reached enlightenment; he mentions that Akuma has come to an awakening of his own. Retsu then showed Gouken the village where the people who killed his father lived; after Gouken told him that he had no intention of fighting them, Retsu told him that his training was complete.

Retsu went out to look for Akuma after promising to find him for Gouken; he first went to Tokyo, only to find that he has no mailing address. He then goes to a village to ask other fighters about him, but was met with stories of how Akuma was the devil incarnate and an evil demon cast from the heavens to bring suffering to humanity; they described him as an inhuman killer of the highest order who revels in sending souls to hell, and a master of pain and death who has killed men, women, and even children. Retsu reports all of this back to Gouken, and suggests that he should forget about him.

At a later point in time, Retsu spars with Ryu to test the boy's skills, and is brutally beaten by Ryu under the influence of the Satsui no Hado, but is stopped by Gouken before Ryu could go too far. As Gouken supervises Retsu's recovery, he tells him that he is fine, and tells Gouken that his student is much stronger then he appears.

Drama CDs
He plays a role in a pair of Street Fighter II Drama CDs released in Japan, "Mad Revenger" and "Portrait of the Magician", where he is voiced by Takeshi Aono.

Trivia

 * Although not connected to Retsu in any way, the character of Makoto is similar to him in terms of fighting style, involving traditional Japanese martial arts with no fireballs, and her background in Street Fighter III is similar to Retsu's background from the original Street Fighter.
 * During the events of Street Fighter Alpha: Generations, Ryu was facing an old man during a fight at the abandoned temple; it has been speculated that this man may have been Retsu.
 * Despite being very significant to the backstory of Street Fighter, Retsu has yet to have made another appearance in a Street Fighter game since the first game.
 * In what was thought to be a piece of artwork for Ultra Street Fighter IV, a character can be seen behind Ryu who bears a striking resemblance to Retsu, which sprung rumors that Retsu was set to be the fifth announced playable character. However, it turned out to be a piece of artwork from the Street Fighter 25th Anniversary artbook, released a year before.