Born January 25, 1937, in NYC, he had described his early life as tough — abandoned as a child by his parents, he was raised by his aunt and considered joining a gang before a chance encounter pointed him toward acting.
While hanging out with a friend who was auditioning, Sierra was asked to improvise and the acting bug bit. He worked with the National Shakespeare Company and in the New York Shakespeare Festival, as well as in other theater, ahead of his 1969 TV debut on "It Takes a Thief."
Sierra made a dizzying array of TV guest spots on shows of the era, including "Medical Center" (1969), "Mod Squad" (1970), and four appearances on "The Flying Nun" (1969-1970) before making his film debut in "Beneath the Planet of the Apes" in 1970.
In 1972, he landed a recurring role as Julio on "Sanford and Son," which allowed Sierra to draw on his Puerto Rican heritage on a show that frequently addressed race and class. Julio was unruffled, a hilarious occasional foil for Redd Foxx's apoplectic Fred Sanford.
While appearing on "Sanford and Son," Sierra continued with other TV and movie roles, including starring as a radical Jewish activist on one of the most shocking episodes of "All in the Family" (1973), which included Sierra's character dying in a car-bomb explosion.
Also during this period, he landed on such hits as "Ironside" (1973), "Kung Fu" (1973), "The Streets of San Francisco" (1973), "Hawaii Five-O" (1973), and "Columbo" (1974), and in the iconic films "Papillon" (1973) and "The Towering Inferno" (1974).
In 1975, Sierra was one of the original cops on the issue-driven sitcom "Barney Miller." Det. Sgt. Chano Amenguale was a groundbreaking Latino professional on TV, one with heart — he breaks into tears on an episode after killing two men in the line of duty.
After two seasons, Sierra was written off the series and given a leading role on "A.E.S. Hudson Street" (1978), but that series flopped after a half dozen episodes, and he was not written back onto "Barney Miller."
One of Sierra's most intriguing parts was as a macho screenwriter in "The Other Side of the Wind," a star-studded film project begun by screen legend Orson Welles in 1970 and that, due to a steady stream of money issues, was abandoned until it was picked up and edited for release in 2018 by the director (and star) Peter Bogdanovich.
Other noteworthy appearances include as zany South American revolutionary Carlos "El Puerco" Valdez on "Soap" (1980-1981), as Lt. Lou Rodriguez on "Miami Vice" (1974), as Lt. Gabriel Caceras on three episodes of "Murder, She Wrote" (1993-1995), as Corbin Entek on "Star Trek: Deep Space Nine" (1994), and in supporting roles in such films as "Honey, I Blew Up the Kid" (1992), "Hot Shots! Part Deux" (1993), "A Low Down Dirty Shame" (1994), and "Mafia!" (1998).
His last screen work was in the TV movie "Blood Money" in 2000, and in a short called "Vic" in 2006.