Another 'Welcome Back, Kotter' Sweathog dies: Ron Palillo

"Oooh! Oooh! Oooh! Mr. Kotter! Mr. Kotter!" "What is it Arnold?" It was a running gag on the weekly hit series of the 1970s, "Welcome Back, Kotter." And now, the second of the four original "Sweathogs" has died.

Ron Palillo, who played the effervescent, nerdish "Arnold Horshack" died of a heart attack early this morning. He was found by his partner of many years, Joseph Gramm. According to TMZ.com, Palillo was rushed to the hospital where he was pronounced dead. He was 63 (which will, no doubt, make many of the show's hardcore fans feel very, very old). "Horshack's" death leaves but two survivors of the orignal Sweathog foursome... John Travolta who played Vinnie Barbarino, and Lawrence Hilton-Jacobs, who played Freddie 'Boom Boom' Washington. Friends tell TMZ that Palillo's death was a surprise as he seemed to be in excellent health, despite being a heavy smoker. TMZ reports the actor had been experiencing a heavy cough as of late, and had, ironically, scheduled a doctor's appointment for today. "Horshack" joins "Juan Epstein" -- played by actor Robert Heyges, who died in January at age 60 -- in the Great Detention Room in the Sky.