Well Capcom never officially and directly tell us, but there are many hints. Like in Street Fighter 4 ending of Akuma and a mini rival conversation where he (Akuma) said "Prepare to meet your maker."
Evil Ryu - Get a character up to levl 31 in tour mode, then play the bonus round in Japan, beat him to keep him Guile - Get a character to levl 31 in World Tour, then beat his bonus stage Shin Akuma - Get a character up to Level 32 in tour mode (MAX LEVEL) face him in the same place as E. Ryu, PS. The Last Bonus Stage; 4 Ryu's 1 Evil Ryu 4 Akumas 1 Shin Akuma (F*****g HARD he can thrown 2 hadokens in the air, i recommend ryu or ken for this challenge
Ryu(Ri-yoo)
Ryu doesn't have a girlfriend
Shorin-ryu, Shotokan, Goji-ryu, kenpo, shito-ryu, wado-ryu
Shin Ryu died in 1680.
Ryu Ota was born in 1930.
Ryu Ota died in 2009.
Ryu Hayabusa was created in 1988.
Ryu Goto was born in 1988.
Jin Ryu is 187 cm.
Ryu Mitsuse was born in 1928.
Ryu Mitsuse died in 1999.