“I’ve lost count of how many times I’ve died,” Monaghan says. “A couple of my deaths didn’t even make it in the final show. But that’s pretty close to the comics. It’s a running theme with him.”

It’s also a field day for writers, who even cut off the character’s head at one point.

Because “Gotham” is an origins story, it’s likely Monaghan’s Joker could age into Nicholson’s or Ledger’s. The Joker he paid the most attention to was Mark Hamill’s in the animated versions.

“What amazes me about him is he tended to shift and change depending on the context he was in,” Monaghan says. “He reinvented the character and made him lighter, darker, more sadistic. That’s what I wanted to do with him – reinvent him, cast him in different lights and see what comes out.”

Because Monaghan also stars on “Shameless,” he had to shift gears when he wasn’t in “Gotham” mode.

“'Shameless’ tends to be more of a reprieve simply because of the nature of that show. It’s an ensemble,” he says, “and I don’t necessarily work every day.” Then, too, Monaghan went from child actor to adult on that series. “It’s been 10 years of growing, with the character and with myself.”