One of Ken's alternate color schemes makes him resemble the character Dante from Capcom's Devil May Cry series. Very fitting since Ken's voice actor, Reuben Langdon, is also the voice of Dante.
Ken's alternate costume, a download for the home consoles, originally started out as the default outfit for the character that would eventually become Rufus.
Incarnations are Street Fighter 4, Super Street Fighter 4, Super Street Fighter 4: Arcade Edition and Ultra Street Fighter 4.
The original game concept, titled Street Fighter IV Flashback, a single-player mode with third-person 3D action that focused on Ryu's backstory, never made it past the proposal stage. Flashback would likewise feature the 2.5D game play and a roster made of classic Street Fighter II characters plus Sakura and a few new characters. Flashback's proposed easy control system was later used in Tatsunoko vs. Capcom: Ultimate All-Stars, minus its titular "flashback" game play feature.
Initially the title had been developed to use 3D hit-boxes, but the testers felt it didn't have the "pixel perfect" precision of a Street Fighter game, and the game was therefore changed to use 2D hit-boxes.