Ron Palillo, best known for playing one of TV's most lovable class clowns on the '70s sitcom Welcome Back, Kotter, died Tuesday at age 63. Palillo starred as goofball Arnold Dingfelder Horshack opposite John Travolta's Vinny Barbarino on the series. His signature catchphrase, "How-wah-ya? I'm Ahhnold Horshaaaack!" never failed to get a laugh. In addition to Kotter, Palillo had roles in The Love Boat, Alice, The A-Team, Matt Houston, and Trapper John, M.D. His agent says he suffered a heart attack and passed away in his sleep.