In an interview with Variety, Bernthal reveals that he wasn't sure he ever wanted to be a superhero or part of one of their universes.
"Fully candid, being part of a superhero franchise was not something that I really had an ambition towards; it wasn't really on my radar," he says. "A lot of the people that I really admire, actors that I really look up to have avoided that whole thing."
But the Punisher isn't exactly a superhero.
"He didn't have any super (powers); he didn't have a mask," he says. "He was a grieving father and husband who was reeling from this unbelievably traumatic event. There was something about that that scared the you-know-what out of me and left me intrigued.
"I always try to gravitate to stuff that scares me," he says. "I love my wife and my kids more than myself. I'd willingly give my life for them. Until you understand love like that, you can understand what it would be like to lose it. Just that kernel of an idea, it scared me."
That trauma, to Bernthal, is what makes Frank Castle interesting and he has no interest in softening the Punisher up to make him a more likely candidate to join the Defenders.
"I'm not interested in making him likable. I'm not interested in making him relatable," he says. "If there was any back-and-forth with me with the powers that be on my show that's where the crux of any argument lay, in saying let's say bold. He's a guy who's living in darkness. He's not trying to win people over."
Whether Bernthal will be able to continue to explore the psyche of Frank Castle remains unclear, as even creator/showrunner Steve Lightfoot doesn't know if Marvel's The Punisher is getting a second season.
"No, I genuinely don't know how the Netflix system works with making those calls, and I assume once they do [make a call] they'll tell Marvel and Marvel will tell me and we'll jump back to it," Lightfoot said in an interview. "But I'm very excited to do so. I think we left both Frank and Billy in places where there are so many ways to jump off from if that second season comes. We can do anything with them, in truth."
Marvel's The Punisher is now streaming on Netflix.