Season 1 - Walter White:
Season 1/2 - Walter White pretending to be Heisenberg:
Season 3/4 (roughly) - Heisenberg:
Season 5 - Heisenberg pretending to be Walter White:
Season 5 - Flash Forward/Post (?) - Heisenberg:
Source of the analysis above: http://imgur.com/a/yC2GZ
Discussion about it on Reddit is excellent:
"Who are you really?" is an ongoing theme in the show.
Walter White knows nothing about being a criminal.
Heisenberg knows nothing about empathy. This is when Hank met Heisenberg:
Hank is REALLY angry with Heisenberg.
Jesse Pinkman has undergone a transformation of his own during the show.
Walter White by ~aerettberg
Walter White transformation gif:
The Evolution of Walter White: