It’s always sad when you lose one of the characters you loved growing up, and today Hollywood is mourning the sudden death of Ron Palillo, who played Arnold Horshack on the 70s TV series “Welcome Back, Kotter.” The 63-year-old actor died at his Palm Beach, FL home from what appears to be a heart attack.

Palillo, who was found unresponsive by his longtime partner Joseph Gramm early Tuesday morning, was rushed to a hospital where he was pronounced dead. The actor, a heavy smoker, had been complaining of a cough and was going to visit a doctor later today.

Palillo is best remembered for his role as Sweathog Arnold Horshack on “Welcome Back, Kotter,” which ran from 1975-1979 and launched the career of John Travolta. Horshack’s trademark was his laugh and the line, “Ooh ooh ooh, Mr. Kotter.”

For the last three years, Palillo had been teaching acting at a Florida academy. Greg Hauptner, founder and CEO of G-Star Academy, gave this statement: “These were 13-, 14-year-old kids [he was teaching], and they didn’t know ‘Welcome Back, Kotter.’ The kids went back and watched just about every episode. It drove him crazy, but he loved every minute of it.”