He also guest starred on many television series during his career, including appearances on Mod Squad, Alias Smith and Jones, Mission: Impossible, Hawaii Five-O, Gunsmoke, The Greatest American Hero, Soap, The Fresh Prince of Bel-Air, The X-Files, Murder, She Wrote and Hill Street Blues.
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He also guest-starred as a Jewish radical in an unusually dramatic episode of All in the Family, working with the Hebrew Defense Association, an organization whose goal it was to stop antisemitism in the neighborhood.
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The actor later went on to star as Dr. Tony Menzies on the unsuccessful sitcom A.E.S. Hudson Street.
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Sierra was cast as South American anti-Communist revolutionary "El Puerco" — whose friends simply call him "El" — on the serial spoof Soap, figuring prominently in the series' unresolved final episode in 1981.
Sierra Leone | Santa Cruz de la Sierra | Gregory Peck | Sierra Nevada | Sierra Club | Sierra Nevada (U.S.) | Gregory of Tours | Order of St. Gregory the Great | Gregory Bateson | Pope Gregory VII | Gregory of Nyssa | Pope Gregory XIII | Sierra Entertainment | Pope Gregory XVI | Ford Sierra | Lady Gregory | Gregory S. Paul | Gregory Corso | Bo, Sierra Leone | Sierra Leone National Premier League | Sierra | Pope Gregory XV | Sierra Nevada de Santa Marta | Sierra Maestra | Sierra Leone People's Party | Sierra Leone Civil War | Gregory of Nazianzus | Special Court for Sierra Leone | Sierra Madre Occidental | Rubén Sierra |
The Wonderful Ice Cream Suit is a 1998 film set in East Los Angeles directed by Stuart Gordon, written by Ray Bradbury and starring Edward James Olmos, Joe Mantegna, Esai Morales, Clifton Collins Jr. (credited as Clifton Gonzalez Gonzalez), Sid Caesar, Howard Morris and Gregory Sierra.