Walt was always an evil POS

There isn’t a moment where Walt “becomes” Heisenberg. There isn’t a moment where Walt reaches this point of no return.

He was always a repressed monster. He clearly has a massive ego, probably because he is constantly (and rightfully) praised for his intellect. All he needed was a life-altering change and then he could let the monster out.

What’s so terrifying is that he’s a sociopath that has spent 50 years learning to mimic normal human behavior. He can easily fake the Flanders type suburban dad.

I think the scene that best shows this is the one with Hank in the garage. Hank realizes that the Walt he thought he knew for 10+ years was the mask and this meth slinging criminal mastermind is the real Walter White.