Ron Palillo, best known as mouthy classroom goofball Arnold Horshack on the 1970s TV series “Welcome Back, Kotter,” died Aug. 14 at his home in Palm Beach Gardens, Fla. He was 63.

He died after an apparent heart attack, said a friend, Karen Poindexter.

Mr. Palillo was inextricably linked with the character he played from 1975 to 1979 on “Kotter,” the hit ABC sitcom, in which title character Gabe Kotter returns to his Brooklyn alma mater to teach a group of lovable wiseguys known as the Sweathogs. Horshack was the nasal teen who yelped, “Oooh, ooh,” and shot his hand skyward whenever Kotter posed a question.

The show’s cast included a young John Travolta as ladies’ man Vinnie Barbarino; Lawrence Hilton-Jacobs played the always cool Freddie “Boom-Boom” Washington; and Robert Hegyes played tough Jewish Puerto Rican wheeler-dealer Juan (Luis Pedro Phillipo de Huevos) Epstein. Hegyes died in January from an apparent heart attack at 60.

The show was a ratings success and pop-culture phenomenon, injecting smart-aleck phrases such as “Up your nose with a rubber hose” into the mainstream and propelling Travolta to stardom. But the series only lasted as long as a high school education and its end, for Mr. Palillo, brought professional difficulty.

A 1978 photo shows “Welcome Back, Kotter” cast members, from left, Lawrence Hilton-Jacobs as Freddy Washington, Ron Palillo as Arnold Horshack, Robert Hegyes as Juan Epstein, foreground, John Travolta, rear, as Vinnie Barbarino. Palillo, best known as the nerdy high schooler Arnold Horshack on the show, died Tuesday in Palm Beach Gardens, Fla., of an apparent heart attack. He was 63. (Uncredited/ASSOCIATED PRESS)

He said he felt exiled throughout the 1980s, unable to find parts, sinking into depression and rarely venturing from his apartment. When offers did come, he felt typecast as Horshack.

Ronald Paolillo was born April 2, 1949, in Cheshire, Conn., eventually dropping the first “o’’ from his surname. His father died of lung cancer when Palillo was 10 and he developed a stutter. His mother thought that getting him involved in local theater might help. He fell in love with the stage and overcame his speech impediment.

He attended the University of Connecticut and earned parts in Shakespearean productions before his big break.

He told interviewers that his dying father’s voice inspired Horshack’s trademark wheezing laugh, but when he auditioned for “Kotter” he thought he’d be passed over for others who had more of a tough-guy New York look. The casting agents knew better, and so did Gabe Kaplan, who played Kotter.

“When Ron walked into the audition and did his first line, ‘Hello, how are you, I’m Arnold Horshack,’ I said ‘That’s him. That’s the guy,’ ” Kaplan recalled in an e-mail to the Associated Press.

Mr. Palillo had been teaching acting classes at G-Star School of the Arts, a charter school in West Palm Beach, for about three years.

“I’ve always felt very at home here,” he told the Palm Beach Post in 2009. “People go out of their way for you in West Palm Beach. They don’t do that in New York.”

Survivors include his partner of 41 years, Joseph Gramm, a retired actor.

— From staff and wire reports