Ron Palillo at the TV Land Awards in 2008. (Mark Mainz/AP)

Ron Palillo — the actor who played Arnold Horshack, the Sweathog with the simultaneously grating and endearing laugh — has died. The “Welcome Back, Kotter” star died early this morning at his home in Palm Beach, Fla. Jackie Stander, Palillo’s agent, confirmed his death to Celebritology and said the cause was a heart attack. He was 63.

Palillo — who was most recently teaching acting classes at G-Star School of the Arts, a charter high school in Palm Beach — had a career that included animated voice work, roles in repertory theater and off-Broadway plays and a famous appearance on “Celebrity Boxing” in which he faced off against “Saved by the Bell’s” Dustin Diamond.

But Palillo will forever be known by most as Arnold Horshack from the enormously popular ’70s sitcom “Welcome Back, Kotter.” As Horshack, Palillo emerged as the most kind-hearted of Gabe Kotter’s bunch of smart-mouthed high school misfits, the one who was always ready with a “Hello, how are ya?” and an “Ooo, ooo” when Mr. Kotter posed a question to which Arnold knew the answer (or thought he did).

At times, Palillo seemed conflicted about his Horshack alter ego. His imdb bio makes absolutely no mention of the role that made him famous; years ago, when this writer interviewed him for an article that ran in a Maryland newspaper, he got frustrated when the “Welcome Back, Kotter” line of questioning ran too long for his liking. He missed a TV Land Awards reunion with his fellow castmates in 2011, but reportedly that was because he was recovering from surgery. He did attend the awards show in 2008, as the picture above indicates.

If he ever tired of being forever associated with that signature laugh, presumably he also knew that his work on the show had guaranteed him a forever-level of fame. As a sitcom character, Palillo’s Horshack was one of the most memorable of the 1970s. His signature catchphrases (“Very impressive, Mr. Kott-errrrrr”) and that New York accent were imitated daily when “Kotter” was at its apex of popularity, and his face was on everything from iron-on T-shirts to metal lunchboxes. Palillo’s portrayal of the scarf-wearing student may have been over-the-top, but it also represented a complete level of comedic commitment that, perhaps, was underappreciated.

Horshack’s “Kotter” co-star Robert Hegyes — who played Juan Epstein, the self-described Puerto Rican Jew who always had a note from his mother — also died earlier this year of a heart attack. He was 60.

That means only two of the Sweathogs are still with us: Lawrence Hilton-Jacobs, who played Freddie “Boom Boom” Washington and, of course, John Travolta, whose role as Vinnie Barbarino catapulted him to a successful film career.

According to the Palm Beach Post, Palillo is survived by his longtime partner, Joseph Gramm.

Greg Hauptner, the founder of the G-Star Academy where Palillo had been teaching, spoke fondly of the late TV star today in that Palm Beach Post story, praising Palillo for his lack of ego and ability to help his students succeed.

“These were 13-, 14-year-old kids, and they didn’t know ‘Welcome Back, Kotter,’ ” he said, adding that “the kids went back and watched just about every episode. It drove him crazy, but he loved every minute of it.”