Fuma Kotaro

A leader of the Fuma ninja. Followed under th Hojo clan during the warring states period in Japan. Believed to have killed the famous ninja Hattori Hanzo in battle. He is usually portrayed as mysterious and dark looking, chaos loving, Hanzo's arch rival, and bent on keeping Japan from being united. He is also shown as a "bad guy" in the game Samurai Warriors 2.

(I personally think he's the coolest character in the game)