Tom Clancy, whose high-tech, cold war thrillers such as The Hunt for Red October and Patriot Games made him the most widely read and influential military novelist of his time, has died. He was 66.

Penguin Group (USA) said on Wednesday Mr. Clancy had died on Tuesday in Baltimore. The publisher did not disclose a cause of death.

Mr. Clancy arrived on best-seller lists in 1984 with The Hunt for Red October. He sold the manuscript to the first publisher he tried, the Naval Institute Press, which had never bought original fiction. A string of other best-sellers soon followed, including Red Storm Rising, Patriot Games, The Cardinal of the Kremlin, Clear and Present Danger, and The Sum of All Fears.

Mr. Clancy had said his dream had been simply to publish a book, hopefully a good one, so that he would be in the Library of Congress catalogue. Four of his books, The Hunt for Red October, Patriot Games, Clear and Present Danger, and The Sum of All Fears were later made into movies, with a fifth based on his desk-jockey CIA hero, Jack Ryan, set for release later this year.

Born in Baltimore on April 12, 1947 to a mailman and his wife, Mr. Clancy entered Loyola College as a physics major, but switched to English as a sophomore, saying later that he wasn’t smart enough for the rigors of science. Ironically, his novels carried stiff doses of scientific data.

After graduation in 1969, he married Wanda and joined her family’s insurance business, all the while scribbling down ideas for a novel. In 1979, he began Patriot Games, in which he invented his hero, CIA agent Jack Ryan. In 1982, he put it aside and started The Hunt For Red October, basing it on a real incident in November 1979, in which a Soviet missile frigate called the Storozhevoy attempted to defect. In real life, the ship didn’t make it, but in Mr. Clancy’s book, the defection is a success.

By a stroke of luck, President Ronald Reagan got Red October as a Christmas gift and quipped at a dinner that he was losing sleep because he couldn’t put the book down — a statement Mr. Clancy later said helped put him on the New York Times best-seller list.