Evil Ryu isn't actually a thing, either. Canonically, Ryu only ever succumbed to the Satsui no Hadou once. It was only for a split second, and it was the same moment Sagat got his famous chest scar (the end of Street Fighter 1). Evil Ryu as a character is supposed to be one of those "what if" scenarios.>>23126235
The Metro City PD was also laughably corrupt at the time. I'm still waiting for Jessica Haggar to show up as a rival to Rainbow Mika Nanakawa.>"Don't think I'm a pushover anymore! Get ready, because just like my father, once I grab you, you're going for a ride!">>23126241
In-canon, Dan's father, Go Hibiki, took Sagat's eye, so Sagat killed him. Dan swore vengeance, but after training for only a day, Gouken threw him out because he wanted vengeance and wasn't taking the lessons seriously. Dan eventually gets his vengeance and beats Sagat but only because Sagat threw the fight just so Dan would leave him alone
. Sakura is also his only known student, but only because he kinda pities him. His style is called Saikyo-ryuu (the Strongest Style).
In reality, Dan was made as a joke towards SNK's Art of Fighting series, because the main characters, Ryo and Robert, were a very obvious knockoff of Ryu and Ken. So Capcom took Robert's head and stuck it on Ryo's body, and bam, Dan was born. Capcom and SNK have had a jolly back-and-forth ever since. In SVC Chaos, half of team SNK keeps confusing Dan for Robert.