Not really, the only obscure thing about him are his motives, and that has been explained as well.
He's an orphan who lost his parents in the war. Inspired by the 3rd and white snakes who shed their skins, he decided to find the forbidden jutsu to make himself immortal, and each himself all the jutsu's there are, most likely because he never wanted to experience war the way he did as a kid.
He only turned against Konoha, after the 3rd denied him as candidate for Hokage, followed by the 3rd discorvering him developing said forbidden jutsus.
The rest is history.
The most mysterious IMO would be Kakuzu, all we know so far still, is that he's a bounty hunter who fough Hashirama.