Back when the development of the "Iron Man" franchise was in its infancy, director Jon Favreau had a problem. He wasn't exactly sure how to make his main character, egotistical genius/superhero Tony Stark, come to life. "I had no idea how to make him seem real," he says in a new write-up on Time.com.

Favreau eventually turned to Robert Downey Jr., the actor hired to play Stark/Iron Man, for some inspiration. "We need to sit down with Elon Musk," he recalled Downey recommending. Turns out, the comparison was spot-on.

"Musk, 38, is a rocket scientist," writes Favreau. "He designed the Falcon 9 booster that may serve as NASA's next vehicle to transport cargo and humans into space. He is also a green pioneer. He helped create Solar City, the largest provider of solar power systems in the U.S. And he designed the Tesla, one of the first electric cars of the modern era. Bob Lutz, the vice chairman of General Motors, credits him with catalyzing GM to move toward electric cars."

With a resume like that, it's not surprising that Musk served as a sort of muse for Tony Stark's on-screen persona. The first "Iron Man" briefly featured a Tesla Roadster parked in Starks' underground shop. But Favreau upped his appreciation in the sequel, in which Musk makes a cameo appearance with Stark, asking if he might be able to design an electric jetpack for him.

I don't care how rich you are — money just can't buy gigs like that. Only superheroes need apply.

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