In the 1st, it seemed he re-enacted something traumatic that happened to him while he freaked out in the basement at the party "You are going to keep this family together, you had better believe it!" "Let me out, let me out!" "Oh he's a good little boy isn't he?" or something like that.
I saw the sequels sooo long ago, and I can't remember if he ever revealed anything more about his past?? Anyone know?
She controlled the animals of the forest even the trees seeming to do her bidding.
Not very much. In part 2, it shows news footage on his arrest. The reporters are saying "before he was Jerry Blake, he was Henry Morrison and before that he was Bill Krieger." Then later on in part 2, the psychiatrist analyzing him refers to O'Quinn's character as "Jerry", the alias he used in part 1. This was wrong, because that clearly was not his real name when knowing that "Jerry" had two different names before. Part 2 should've had the shrink referring to "Jerry" by his original birth-name, which would've quite possibly been Bill Krieger since that was "Jerry's" name before he changed it to Henry Morrison. Considering "Jerry's" age, how many times could he have killed before changing his identity twice? That's just my theory. But part 2 should've done more than just hint or imply, it should've fully stated who he was originally and had the shrink referring to him as that. That would've made part 2's plot deeper.
I heard that The Stepfather was intended to be only one film. It became a sleeper hit. I agree that the threapist in the second film should have called him Bill instead of Jerry. I do believe Jerry was reliving a moment when he freaked out in the basement in the first film, most likely from his childhood.