Well, he is a stupid old man who believes the secret to peace is to give one of two warring clans unrivalled power, then giving the other clan the same power when it doesn't work. He once devastated the planet by gouging a moon sized hole out of it in order to seal a monster he could have sealed far easier. he has created at least twelve different ways for humans to kill each other (Indra powers, Ashura powers, Nine tailed beasts and good old ninjutsu). He is bent on wiping out ninjutsu by destroying everyone who practices it using the Yin-Yang seals, and he is likely the worst parent in the history of manga, having given one of his children godlike power in the knowledge that they would use it to kill the other one. twice.
Oh, and he smiles in a creepy way that people think makes him evil, as apposed to everything else.
