Ronald Gabriel Palillo 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).

Welcome Back, Kotter is an American sitcom starring Gabe Kaplan as a high-school teacher in charge of a racially and ethnically diverse remedial education class called the "Sweathogs." Recorded in front of a live studio audience, the series aired on ABC from September 9, 1975, through May 17, 1979. It provided John Travolta with his breakthrough role.