Aaron Copland, the immigrants' son from Brooklyn who used jazz rhythms of the South, folk songs of Appalachia and cowboy tunes of the prairie to create classical music that was unmistakably American, has died at 90.

The composer, who lived in Peekskill, died Sunday at Phelps Memorial Hospital in North Tarrytown of pneumonia. He had suffered two strokes recently.The "dean of American music" created such classics as "Appalachian Spring," "Rodeo," "Billy the Kid" and "Lincoln Portrait." Leonard Bernstein once called Copland's 1942 orchestral composition "Fanfare for the Common Man" the "all-time top of the hit parade in American music."

The son of Eastern European immigrants, he strove to be more American than most Americans and sought to focus the international spotlight on his fellow American composers.

"He put American music on the map. He decided that there should be an American sound, a place for the American composer," Vivian Perlis, who collaborated with the composer on his 1984 memoir, "Copland," said Sunday.

Copland wrote two operas, six ballets and eight film scores, including his Oscar-winning music for William Wyler's "The Heiress" in 1948.

He won a Pulitzer Prize in 1945 for the ballet "Appalachian Spring," based on a Shaker melody played on a clarinet. It was choreographed by Martha Graham.

His ballets "Billy the Kid" in 1938 and "Rodeo" in 1942 make use of cowboy tunes and folk songs.

Other works included the score for "The Red Pony," the 1949 movie based on the novel by John Steinbeck, and "Lincoln Portrait," music performed with narration inspired by the writings of Lincoln biographer Carl Sandburg. The Jewish boy from New York who learned to write cowboy-inspired classical music didn't even travel to the West until he was 28.

"I preferred to imagine being on a horse without actually getting on one!" he once said.

William Schuman, who with Bernstein and Copland formed what Schuman called a triumvirate of American composers, said, "Copland believed in the validity of American music, that we were not inferior to our European cousins."

"He created the American sound in symphonic music," said Schuman.

Both Bernstein and Copland "wanted to incorporate popular music into concert music. They wanted it to be in contact with people," said composer Elliott Carter.

Copland's storekeeper parents initially were reluctant to pay for music lessons. "My parents were of the opinion that enough money had been invested in the musical training of the four older children, with meager results," he recalled.

But his persistence prevailed, and Copland eventually studied in Paris with Nadia Boulanger and sold a composition, "The Cat and the Mouse," for $32.50.

"To finally see my music printed means more to me than any debut in Carnegie Hall," he wrote home.

With such jazz-inspired creations as "Piano Concerto" in 1926, Copland once said, "I felt I had gone to the extreme of where jazz could take me, the audiences and critics in Boston all thought I had gone too far."

During a trip west, Copland heard the piece being hissed during rehearsal and again in concert at the Hollywood Bowl. But he forged on, experimenting with even more complex rhythms.

"Symphonic Ode," which premiered in 1932, was so difficult conductor Serge Koussevitzky told Copland it took an hour to rehearse three bars.

Then, in 1936, Copland did a musical about-turn - to a simpler, folk-based style in "El Salon Mexico," inspired by a visit to Mexico City. The work was followed in 1942 by "Rodeo," which launched Agnes DeMille's dancing career.

Copland, who never married, is survived by several nieces and nephews. Funeral arrangements are pending.