Setting
The game takes place after the Street Fighter II tournament, but before Street Fighter III.
Characters
The arcade version of Street Fighter IV features all twelve World Warriors from the original Street Fighter II as part of the regular roster, along with four new characters (C. Viper, Rufus, Abel and El Fuerte). The game also introduces a new non-selectable boss character named Seth.
Two hidden characters are featured in the game. One of them is Akuma, who is both, a hidden challenger, as well as secret selectable character. The other is Gouken, Ryu and Ken's sensei, making his official debut in a fighting game. As of October 2008, Gouken appears only as a secret challenger and is not selectable.
The home versions will feature all the characters from the arcade, as well Fei-Long, Dan, Sakura, Rose, Cammy and Gen. Seth can be unlocked as a playable character in the home version of the game, too.