What TV character had the best, well-written and understandable redemption arc?

Prince Zuko

Maybe cheating a bit, but Loki. His arc in the movies is cool, but the series really nailed it down.

I think Resident Alien is a close 2nd.

Dr Mckay from Stargate Atlantis. Dude came in with an ego the size of the new galaxy.

Mr Belvedere

Walter White