Ray Bradbury, a master of science fiction whose lyrical evocations of the future reflected both the optimism and the anxieties of his own postwar America, died on Tuesday in Los Angeles. He was 91.

His death was confirmed by his agent, Michael Congdon.

By many estimations Mr. Bradbury was the writer most responsible for bringing modern science fiction into the literary mainstream. His name would appear near the top of any list of major science-fiction writers of the 20th century, beside those of Isaac Asimov, Arthur C. Clarke, Robert A. Heinlein and the Polish author Stanislaw Lem....