Sitcom sidekick no more. Best known for his supporting role as Andy Dwyer on NBC’s Parks and Recreation, Chris Pratt is poised to break out in a big way with the release of Marvel’s Guardians of the Galaxy on Friday. The movie co-stars both Bradley Cooper and Zoe Saldana, but as the main hero Pratt has become the more public face of the film, endearing himself to fans with his honest assessments of just what it takes to play a superhero.

In a Monday night interview with Nightline, the film director James Gunn admitted that when Pratt’s name came up, his first thought was, “there’s no way.” However, he related that “within 20 seconds of [Pratt’s] audition this is absolutely the guy…. Chris Pratt is the biggest movie star in the world. It’s just people don’t know it yet.”

Pratt acknowledges the studio took some extra steps to ensure he was committed to looking the part. Initially much heavier—the actor told David Letterman he started at 290 pounds—he participated in serious training and dietary changes to fit the role, all under Marvel’s supervision.

“They would send someone over to my house to measure me every week,” he said. “It was like I was on The Biggest Loser.”

Despite the hard work, Pratt feels grateful for the change in his career.

“I used to be a door-to-door-salesman. I lived in a van,” he asserts. “I’m a f—ing Hollywood movie star now…I’ve got nothing to complain about.”