Giorgio Tozzi, an operatic bass who performed dozens of roles with New York’s Metropolitan Opera and whose dubbed singing can be heard in the popular 1958 movie “South Pacific,” died May 30 in Bloomington, Ind., after a heart attack. He was 88.

Mr. Tozzi transcended the bass’s typically anonymous, supportive roles to become an opera headliner in his own right. He mastered more than 60 roles during his career and was perhaps best known for portraying the title characters in Mozart’s “Don Giovanni” and Modest Mussorgsky’s “Boris Godunov,” and Hans Sachs in Richard Wagner’s “Die Meistersinger” and Figaro in Mozart’s “The Marriage of Figaro.”

Unlike many classically trained singers, Mr. Tozzi eagerly dabbled in musical theater. In 1957, he played Emile de Becque, the lead male role in Rodgers and Hammerstein’s “South Pacific,” opposite Mary Martin in San Francisco. When the film version was made, Mr. Tozzi dubbed Rossano Brazzi’s singing parts, including two of the show’s most memorable songs, “Some Enchanted Evening” and “This Nearly Was Mine.”

In 1979, Mr. Tozzi starred in a Broadway revival of Frank Loesser’s “The Most Happy Fella” and was nominated for a Tony Award as best actor.

His preferred venue, however, was always the operatic stage, where the 6-foot-2 Mr. Tozzi had a commanding presence and a voice once praised by a New York Times critic for its “mellow, velvety smoothness.”

He made his Metropolitan Opera debut in 1955, two years after he first performed at La Scala, the renowned opera house in Milan. He appeared at most of the world’s leading opera venues and shared the stage with many of the great sopranos of the 20th century, including Maria Callas, Renata Tebaldi, Roberta Peters and Joan Sutherland.

Mr. Tozzi was known for making his singing sound effortless, but he pointed that he had to “sweat blood over every phrase.”

Often asked what part of Italy he was from, Mr. Tozzi proudly replied, “Chicago,” where he was born Jan. 8, 1923. His Italian immigrant parents named him George John Tozzi.

He did some amateur singing in his teens and studied biology at Chicago’s DePaul University before serving in the Army during World War II. After the war, he began to take up singing in earnest and occasionally performed in choruses and nightclubs.

He appeared in a 1948 New York production of Benjamin Britten’s opera “The Rape of Lucretia” opposite Kitty Carlisle. A year later, he was on London’s West End in a musical, “Tough at the Top,” as a boxer who falls in love with a princess.

“What I remember most was a scene in which I had to sing and box at the same time,” he told the New York Times in 1961. “If you think that’s easy, try it.”

He then moved to Milan, where he shared a fifth-floor walkup and led an impoverished life as an opera student. He sold his camera, his luggage and, finally, some of his clothing as his weight dropped from 200 pounds to 148.

The privation of Mr. Tozzi’s life in Italy proved to be valuable training for one of his later roles as Colline in Puccini’s “La Boheme,” who sings the aria “Vecchia zimarra” about pawning his coat.

He learned to speak Italian and by the time he returned to the United States, George Tozzi had become Giorgio. In 1954, he married a Montana-born singer he met in Italy, Catherine Dieringer. She died in 1963.

Survivors include his second wife, singer Monte Amundsen, whom he married in 1967; two children from his second marriage; and three grandchildren.

Mr. Tozzi, who retired from the Metropolitan Opera in 1975, sang the role of Boris Godunov in a 1961 NBC television production and appeared in a televised performance in 1978 of Gian Carlo Menotti’s “Amahl and the Night Visitors.”

He often appeared in regional productions of “Fiddler on the Roof,” “Man of La Mancha,” “Fanny” and other musicals, and had straight acting roles in several television shows, including “The Odd Couple,” “Baretta,” “Kojak” and the 1976 miniseries “Captains and the Kings.”

Mr. Tozzi taught at the Juilliard School in New York for many years and later at Indiana University.

His hobbies included photography and carpentry.

“Nothing takes your mind off music,” he once said, “as fast as a hammer landing on your thumb.”