Howard signed on for the role when he was 17 in a desperate bid to avoid the U.S. draft.

"I'd already been accepted to USC (University of Southern California) Film School but my draft number was 41, and that's a bad draft number and there were no more deferments and I thought, 'Well I don't really wanna fight, I don't really wanna go to Canada, I really wanna be a director...' he tells sports host Dan Patrick.

"I thought that somehow Paramount Studios and ABC will figure out how to keep me outta the jungle if I'm on their TV show."

But the pilot wasn't picked up and Cunningham went off to film school and forgot about Happy Days - until his movie American Graffiti became an unexpected hit.

"It was about the 60s, and ABC went back and said, 'Now, we need to do a show about the 50s or 60s', and Garry Marshall, who had created Happy Days, said, 'As a matter of fact, we have it and the same guy who was in the movie you liked... was in our show'," Howard recalls.

"You know, the b**tards still made me audition again. I had to test again for my own part! It's a rough world."