"I never in a million years fancied myself playing a superhero," the actress, who stars as the would-be superheroine–turned–gritty private eye in Marvel's Jessica Jones, tells PEOPLE. "I don't look like superheroes that we've all seen in that female form with the outfit and the boobs and the big hair – that's just not me."
But Ritter, who previously demonstrated her dramatic skills in Breaking Bad and her comedic chops in Don't Trust the B---- In Apt. 23, says once she learned about the edgy, smart-mouthed comic book character without a costume or a code-name, she knew she may have found the role of a lifetime. The latest in a string of series based on Marvel Comics' street-level crimefighters began streaming on Netflix Friday.
Because she enjoys auditioning, Ritter was willing to read for the series – which starts with the extra-strong Jessica Jones trying to move forward after a dark traumatic encounter that ended her brief attempt at heroics.
"I was like, 'Well, I'm never going to get that.' And my manager was like, 'No, no – it's actually really right for you: she's a superhero, but she's really bad at it,' " says Ritter. "So in my mind, I'm like, 'Is this like a slapstick comedy? What is this?' I went in knowing so little about the part. I had no idea what was in store for me."
But, after adhering to Marvel's famously strict security measures and reading the script in a locked room without her phone, "I walked out and said, 'Obviously, I have to play her,' " Ritter says with a laugh. "I felt it was just a massive opportunity for me to get to do everything, all in one role. In the past, I've had opportunities to be funny or be more dramatic in things, but never once have I had an opportunity like this where I literally got to use everything I've got."
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Part of the appeal was the lack of the usual superhero accoutrements.
"She was never going to be in a costume, and she was never going to be seen flying over the city with her arms spread out. It was never going to be like that, and I don't know that I would be the girl to do all of that," the actress says. "What I love about Jessica Jones is she has her feet on the ground. I just play her like a real person who also happens to have these superpowers."
Ritter was happy to get hands-on in helping craft Jones' signature street look – scruffy, rumpled and determinedly unfashionable.
"I was very involved with that look and how I needed to feel in order to inhabit her and have that physicality," she says. "So for her, the clothes live on the floor. I barely change my outfit. She doesn't have any money, so I just wanted that to feel really authentic."
She stresses that she never wanted the character to be "sexualized and in high heels" or "using her sexuality to get what she wants." "If Jessica Jones is sexy, it's only because of her attitude," says Ritter.
The role also doesn't require the intense fighting skills of characters like Black Widow or Captain America. Even with her superhuman strength, Jessica Jones is a street brawler.
"I got really good at throwing a punch," says Ritter. "I have a great right hook. I can do a lot of push-ups. I've got into seriously sick shape to do this part! When we wrapped, I stopped working out immediately because I needed a break. But it was really empowering for me to just get into that kind of physical condition."
The role is not only be the centerpiece of her own series. She'll also join with Netflix's other Marvel heroes, including Daredevil and Luke Cage, for an Avengers-style team-up, The Defenders.
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"I just wanted to prove to them every day that they picked the right girl, and with me, they were getting a work ethic that they would find nowhere else. So I wanted it so badly, that I just worked my ass off."
Jessica Jones is now streaming on Netflix.