Henry Winkler knew how to play it cool as Arthur "Fonzie" Fonzarelli on the 1970s sitcom Happy Days, but friends and family members say the actor's tough-guy swagger was all just an act.

"Henry did not have the self-confidence," recalls wife Stacey on an upcoming A&E Biography (airing June 19). "It was always, 'Was I OK?' He was nervous a lot of the time. He was very insecure."

Happy Days co-star Ron Howard (Richie Cunningham) says the Fonzie character that audiences saw at home was nothing like the Yale-trained, serious actor he got to know off-camera. "Fonzie was this kind of big, bold, vivid character and Henry is a mild, gentle, intellectual man," he explains.

Despite Winkler's insecurities, Happy Days hit it big and drew an estimated 65 million viewers a week. And Winkler, whose popular Fonzie character was originally meant to be a supporting role, suddenly found himself sharing top billing with Howard.

"There were some challenges there for me because Richie Cunningham was the lead of the show and that's sort of why I did the show," admits Howard. "My ego was being challenged from time to time and Henry was nothing but understanding and respectful."

In recent years Winkler has continued to find work as both an actor (Scream, The Waterboy) and as a TV producer (MacGyver). Says actor pal John Ritter: "He might be scared, he might be insecure, but he goes ahead and does it."