when did willy woz become a troll?

[Eraserhead]

He always was and always has been a quasi-troll but ebb and flows through bouts of seriousness. He might turn toward seriousness slightly for awhile, and then return to being a troll.

That basically sums it up and he's even admitted this himself. I think he's starting to go through another troll phase now but he's harmless anyway, so who cares.