Talking to Observer, he said that we'll see more of why the Joker (Joaquin Phoenix) is the way he is:
"I think it’s going to be very different [from previous versions] because it really goes into just the origin story. Villains are never born that way, they’re made. There’s something that happens in their lives that they give up their faith in humanity; they see the flaws of humanity and mankind and feel like they must correct it. And what happens with Joker is you start to see how he really was a happy person. He really was trying to find this…hope in humanity until it broke him down and he just had to give up and reshape it.
Also, there’s going to be a connection [made] about a boy and his mother. That is another thing that you’re going to see—that he was capable of love at some point. But, at the end of the day, I think it’s all about how he was made that way, how he didn’t start being that kind of person."
Frances Conroy is listed as playing "Penny Fleck" in the film (the Joker's real name here is "Arthur Fleck"), so we look forward to seeing what she'll do with the part.
The actor also talked what we can expect in the sequel to "A Quiet Place," which he just signed onto:
I’m still trying to find that out, but I really think that what we’ll do is we’ll see more of that family continuing to survive and finding out that they’re not the only ones. And I think that we’re also going to get a few answers to the origin of where and how this whole thing happened. I think that people want to know that. But I think you’re just going to see another side of it…more of humanity that survived this thing in this next story.