Born in Puerto Rico as Rosa Delores Alverio, Moreno and her mother moved to the USA when she was a toddler. Almost immediately, the youngster began a performing career, appearing in shows at Macy's. By the time she was a teenager, Moreno was acting on Broadway (1945's "Skydrift"). Four years later, she was spotted by a Hollywood casting agent at a dance recital and whisked to Tinseltown with an MGM contract in hand. As the film industry rarely knew what to do with talented non-white performers, Moreno was relegated to a playing stereotypical Latina spitfires and Indian maidens in a spate of B-movies. A rare opportunity came when she was chosen to tango with Gene Kelly in the now classic "Singin' in the Rain" (1952) but her first major break came when she landed the role of Tuptim, the rebellious concubine of the Siamese monarch in "The King and I" (1956). Encouraged by co-star Yul Brynner, she studied with an acting coach and her hard work finally paid off with 1961's "West Side Story". As the fiery Anita, who sings and dances the show-stopping "America", Moreno blazed across the screen netting that year's Best Supporting Actress Academy Award.
Her post-Oscar films, though, proved unspectacular and hardly challenged this gifted player. Instead, Moreno turned to the stage, making her London debut in "She Loves Me" and appearing on Broadway in "The Sign in Sidney Brustein's Window" (both 1964). After time out for motherhood, she returned to the big screen opposite her former lover Marlon Brando in the ludicrous "The Night After the Following Day" (1968) before beginning to hit her stride as Alan Arkin's girlfriend in "Popi" (1969). While co-star Ann-Margret garnered the lion's share of critical kudos for "Carnal Knowledge" (1971), Moreno was equally effective in her all too brief scenes as a prostitute hired by Jack Nicholson. Switching gears, she spent the next five years as a company member of the children's educational program "The Electric Company". In 1975, Moreno had great fun spoofing the Latina spitfires of her earlier career as Googie Gomez, a second-rate Puerto Rican entertainer in a gay bathhouse, in Terrence McNally's play "The Ritz". Richard Lester wisely chose to allow the actress to preserve her Tony-winning turn in the following year's film adaptation. She rounded out the 70s with a pair of Emmy Awards, one for a 1975 guest appearance on "The Muppet Show" (syndicated) and the second as a reformed hooker in a memorable 1978 episode of NBC's "The Rockford Files". (This was the second of four appearances on the series and she would later reprise the part for a 1999 CBS TV-movie sequel.)
While the 80s saw Moreno's film career dwindle--her last role for nearly a decade was in Alan Alda's warm study of middle-aged friendships "The Four Seasons" (1981), the stage and TV picked up the slack. She inherited Lily Tomlin's role of Violet Newstead for the ABC sitcom version of "9 to 5" (1982-83), headlined a busted 1986 pilot for her own sitcom and had a regular role as Burt Reynolds' ex-wife in "B.L. Stryker" (ABC, 1989-90). In between small screen gigs, she performed her own one-woman variety concert and toured with Sally Struthers in a distaff version of Neil Simon's "The Odd Couple" (1984-85) which also included a stop on Broadway.
Resuming her film career in 1991, Moreno played Jonathan Silverman's mother in the uneven "Age Isn't Everything/Life in the Food Chain". She contributed memorable work as Jon Seda's highly critical mother in Darnell Martin's "I Like It Like That" (1994) and was reunited with Alan Arkin as his snooty sister-in-law in "Slums of Beverly Hills" (1998). While continuing to play her one-person show, Moreno also made theater history in 1996 as the first Latina to play silent screen star Norma Desmond in the London production of Andrew Lloyd Webber's musicalization of "Sunset Boulevard". The actress also found a new round of fans playing Sister Peter Marie, a nun and the psychological counselor to the inmates of a maximum security facility, in "Oz" (HBO, 1997- ). In 2001, she earned plaudits for her turn as the title character's mother who instills in him a love of words in the biopic "Pinero".