Walter White has undergone an amazing character transformation in just 61 episodes. Wow.

"You see, technically, chemistry is the study of matter, but I prefer to see it as the study of change: Electrons change their energy levels. Molecules change their bonds. Elements combine and change into compounds. But that's all of life, right? It's the constant, it's the cycle. It's solution, dissolution. Just over and over and over. It is growth, then decay, then transformation. It is fascinating, really."  ~Walter White, Season 1, Ep. 1, "Pilot"

More on the transformation of Walter White:

http://pandawhale.com/post/24774/bryan-cranston-has-portrayed-5-distinct-characters-from-walter-white-to-heisenberg-in-breaking-bad