IN LATE 1934 George Gershwin, in the process of creating his masterwork, Porgy and Bess, wrote to the librettist DuBose Heyward:

Here is an exciting bit of news. I heard about a man singer who teaches music in Washington and arranged for him to come and sing for me. In my opinion he is the closest to a coloured Tibbett I have ever heard. He is about six foot tall and very well proportioned with a rich, booming voice. He would make a superb Crown and, I think, just as good a Porgy.

The composer had in fact found his Porgy. Gershwin had originally been so taken with the idea of starring Lawrence Tibbett, then at the height of his fame as a baritone at the Metropolitan Opera House, that he had considered having Tibbett perform in blackface, but his discovery of Duncan solved all problems. Duncan, like his Bess (Anne Brown) and the rest of the opera's cast, was not experienced on the operatic stage but, the lyricist Ira Gershwin later said, "brought a humour and pathos to the role which helped considerably to humanise Porgy, making him dignified but not maudlin".

For his part, Duncan was not sure that he wanted to sing Gershwin. "I was a bit of a stuffed shirt," he stated later, "and thought of George Gershwin as being Tin Pan Alley and something beneath me."

He was born Robert Todd Duncan in 1903 in Danville, Kentucky, and attended Butler University and the College of Music and Fine Arts in Indianapolis, receiving a master's degree in voice from Columbia University. In 1929 he went to New York to study, becoming a Professor of Voice at Howard University in Washington DC in 1931.

It was while singing the role of Alfio in an all-black production of Cavalleria Rusticana at the Mecca Temple on 55th Street, New York, that he was heard by the music critic Olin Downes, who recommended him to Gershwin. At his audition he sang a little-known Italian aria by Secchi, "Lungi Dal Caro Bene", which impressed the composer. "Every other singer," said Gershwin, "had sung spirituals or `Old Man River'."

When Gershwin said to him, "Will you be my Porgy?" the wary Duncan replied, "I don't know, I'd have to hear your music." When George and Ira later performed their Porgy songs for Duncan be had no doubts. "I was in heaven," he said. "Those beautiful melodies in this new idiom - it was something I had never heard. By the time they got to Porgy's final song `I'm On My Way' I was weeping." He wrote in a letter to Gershwin, "I have seriously worked on my art for years waiting for a serious work like this, open to the serious Negro artists."

Directed by Rouben Mamoulian, Porgy and Bess opened on 10 October 1935 in New York and had a mixed reception - while drama critics generally praised the piece, music critics were worried about its hybrid nature and the presence of hit tunes which they felt compromised its position as an opera. It ran for a modest 134 performanecs. When it was revived in 1942, again with Duncan and Browne as leads, audiences had come to know many of its great songs and with recitatives cut and a smaller production it was a hit, running for 35 weeks and touring successfully.

In between these productions, Duncan had starred in London opposite Edna Best in the thriller The Sun Never Sets, and in 1941, at the request of the director Mamoulian, he had played the Lord's Messenger, sent to earth to encourage the reformation of the gambler "Little Joe", in the Vernon Duke / John Latouche hit Cabin in the Sky. Four years later Duncan became the first black artist to appear with the New York City Opera when he sang the role of Tonio in Pagliacci.

When Alan Paton's poetic novel set in South Africa, Cry the Beloved Country, was turned into a Broadway musical, Lost in the Stars, by Kurt Weill and Maxwell Anderson in 1949 (with Mamoulian again as director), Duncan starred as the preacher who forms a bond with the father of a young white liberal who has been killed by the preacher's son. Though the static and harrowing show was not commercially successful, Duncan's songs included the popular title number and the critic Robert Garland wrote: "The beauty and simplicity of Cry the Beloved Country infrequently comes through. Only Todd Duncan seems to sense the novel's artful artlessness."

The show was Duncan's last, but in the 1955 film Unchained he played the inmate of a minimum security prison and introduced the hit song "Unchained Melody", which was nominated for an Academy Award.

Duncan continued to teach at Howard University and as a concert singer performed arias and Lieder in more than 2,000 performances in 56 countries. Married since 1934 to Gladys Jackson, a teacher, he continued to give singing lessons at his home in Washington until recently.

Robert Todd Duncan, singer: born Danville, Kentucky 12 February 1903; married 1934 Gladys Jackson (one son); died Washington DC 28 February 1998.