Evil Ryu is an alternate form of Ryu who is heartless, mad, uncontrollable, and nothing more than a demon.
Evil Ryu enjoys absolute power and obsesses with fighting and will defeat any fighters standing in front of him with no empathy or respect. In Street Fighter IV he takes on a much more menacing and powerful appearance, with a gaping hole burned into his chest and his back that bears a glowing "Heaven"(天) Kanji.