Ronald Gabriel Palillo (April 2, 1949 – August 14, 2012) was an American actor and teacher. He was best known for his role as the endearingly dim-witted character Arnold Horshack on the ABC sitcom Welcome Back, Kotter (1975–1979).
Ronald Gabriel Paolillo was born in New Haven, Connecticut, to Italian-Americans Gabriel and Carmel Paolillo, and raised in nearby Cheshire. He graduated from Cheshire High School and the University of Connecticut at Storrs, where he would teach in the 1990s. He attended Fairfield University while pursuing a postgraduate degree. He adopted the last name Palillo for his acting career.
In 1975, Palillo was cast as Arnold Horshack, one of the misfit "sweathogs" in the high school sitcom Welcome Back, Kotter, whose antics made him one of the standout characters of the series. In the last season of the series, a backdoor pilot episode for a spin-off series featuring Horshack was produced, but the series was not developed.

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