Elisabeth Moss signed up for The Handmaid's Tale because of "pure jealousy and competitiveness".
The 36-year-old actress was initially going to turn down the role of June (aka Offred and Ofjoseph) in the dystopian drama series but changed her mind after a "nightmarish experience" of visualising someone else in the part.
She told Heat magazine: "The problem was that I didn't want to sign on necessarily to do another TV show so quickly, as it had only been a couple of years since I worked on Mad Men.
"But I was thinking about whether to do the show one evening and I remember having an almost nightmarish experience of waking up in the middle of the night imagining not taking it and someone else doing it.
"I pictured that in my mind and then I thought to myself, 'No, no, no, no, no someone else is not getting their hands on this. So I said yes.
"That's why I did it - pure jealousy and competitiveness.
"I'm so glad I did though, and it's been the role I've felt most connected to out of anything I've ever done. I'm so proud to have been a part of it."
The former Mad Men star admitted she finds "dark" characters and subjects compelling and doesn't get too "tormented" by her bleak roles.
She told the magazine: "I've always found darker stories and characters more compelling, although I'm not really sure why I'm drawn to them.
"I'm not someone who takes their work that seriously though, so I'm able to step in and out of my characters very easily.
"I don't let playing a dark character torment me and I don't need to torment myself to play someone like June either."