Ron Palillo, who played sweathog Arnold Horshack on 'Welcome Back, Kotter,' has died at 63.

He was found by his longtime partner early Tuesday morning in their Palm Beach, FL home, victim of an apparent heart attack.

Palillo got his start as a Shakespearean actor, but his first and most-lasting movie or TV credit was 'Welcome Back, Kotter.' His Arnold Horshack character, known for his unique laugh and for raising his hand and calling out "Ooh ooh ooh, Mr. Kotter!," was the class cut-up in the beloved sitcom which also featured a young John Travolta. Palillo's fellow costar Robert Hegyes, aka Epstein, passed away earlier this year.

After 'Kotter' went off the air in 1979, Palillo popped up as a guest star on '80s staples like 'Laverne & Shirley,' 'ChiPs' and 'Murder, She Wrote.'

Palillo also illustrated two children's books, and lately has been involved in plays and independent films around Palm Beach and his birth state of Connecticut.

But, of course, the public will most remember Palillo as Horshack. Here a few clips of his portrayal of the classic sitcom character.

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