I have a theory, about the Jokers dad, that
I (could possibly, if my theory is correct and could work.) know who his father really is. I believe the Jokers dad is Joe Chill, it one works with the Dark Knight movies which I technically guess you could say aren't cannon, but for the sake of my theory lets just say it is. The Joker has many pasts that we somewhat know of and also have no idea about. But I believe that for one in the Dark Knight movie, that the reason he had gotten those cheek scars was from his father Joe Chill, in the dark knight Joker had mentioned that his father came home one night, "crazier then usual." And that set everything in motion with his mother being killed, and then his father giving Joker those nasty cheek scars. But let's rewind for a moment to why he came home "crazier then usual" I believe that Joe killed Bruce Wayne's parents, and he was paid to do it, (and for that reason is for other theories.)
After he was done with the killings, he went to a bar, gotten drunk. Like mad drunk, and then came home, "crazier then usual." And that set both of those boys fates into action. Now I know some people will say "but he also had another reason he got those scars!" But for the sake of my theory lets just say that isn't true, and he himself doesn't really even know his own past. So again, let's just say it was his dad. Now let me also tell you how I feel it could work in the comic books, and outside of the Dark Knight movie, Joe Chill is in both as is the Joker, but not Jokers scars. Well that doesn't really make a big difference, scars or no scars Joker is still crazy as can be. Joker never really gave an explanation to why he's so fascinated with batman, yes I mean he's said things like "this was always meant to happen." But really lets take a deeper look at the meaning of the reason, I mean why does he say that? I feel it's because he knew that Batman stopped his father, and that's really the connection that draws him to Batman, I mean nothing says he hated his father, or anything, but again it would make sense. The Joker in the killing joke back story, when he fell into Ace chemicals, and went crazy, it must've triggered something, that just made him love Batman for doing that. I mean I know it sounds a bit crazy, but isn't that what comics are all about. I also noticed something that could back up my theory strangely, in The Batman: Death of the Family, you see Joker with work clothes on that says, Joe's garage, and also the name tag, Joe. I think that his dad use to own a business, Joe's Garage. Lets just say in the year he went missing he went back home, and got all his fathers old work stuff. But near the end of the book that's how batman found out who he was. He made the connection. But that's unknown because we all know Joker stops him from saying anything more. I believe that in all facts that I've provided, Jokers dad is Joe Chill.