Viper is the "Leader" of Kagekenin (He isn't really the leader Gensho is), as well as its Strongest, Fastest, and most Defensive member. He is also the strongest Sharingan user alive. His regular three-tomoe Sharingan can look through any Genjutsu. That makes his Mangekyo Sharingan more powerful than any eye technique around. He being an Uchiha makes him a Fire Style and Fire Element master. Viper wants the Ten Tailed Jinchuriki for his student, so the Jinchuriki can be the Uchiha heir and the strongest eye technique user in the world. This added to the Ten Tails’ power will make him the strongest Jinchuriki on Earth.