Ron Palillo, who played Horshack on the 1970s sitcom WELCOME BACK, KOTTER is dead at 63, according to TMZ.
Palillo's character was known for the way he caught Mr. Kotter's attention in class with his, "Oh! Oh! Oh! Mr. Kotter!" on the show that ran from 1975 to 1979.
After the show was canceled, Palillo appeared at as guest star on television shows throughout the 1980s and 1990s, such as CAGNEY & LACEY, and did voice work in cartoons.
In 1994, he appeared as underhanded blackjack dealer Gary Warren in ONE LIFE TO LIVE.
Robert Hegyes, who played Juan Epstein on the show, died earlier this year on January. 26, 2012. The cast of WELCOME BACK, KOTTER, including John Travolta, reunited at the TVLand Awards last year.