Tom Clancy, the bestselling U.S. author of popular spy and military-themed thrillers such as "The Hunt for Red October" and "Patriot Games," has died at the age of 66.

Clancy's publisher, G.P. Putnam's Sons, confirmed to The New York Times that Clancy died in a Baltimore hospital on Tuesday. The cause of death was not provided.

Clancy first came to international attention in 1984, after selling his thriller "The Hunt for Red October," to the first publisher he solicited: the Naval Institute Press. Clancy's book was the first novel the publisher had ever released.

The book enjoyed widespread success, with then U.S. President Ronald Reagan even saying he was losing sleep because he couldn't stop reading it -- a statement Clancy later said helped put him on the New York Times bestseller list.

"What happened to me was pure dumb luck. I'm not the new Hemingway," Clancy later said in an interview with the American Movie Channel.

Other bestsellers soon followed, including "Red Storm Rising," "Patriot Games," "The Cardinal of the Kremlin," "Clear and Present Danger," "The Sum of All Fears," and "Without Remorse."

Clancy once said that he thought of himself as a storyteller, not a writer.

"I think about the characters I've created, and then I sit down and start typing and see what they will do. There's a lot of subconscious thought that goes on. It amazes me to find out, a few chapters later, why I put someone in a certain place when I did. It's spooky," he said.

Penguin Group CEO David Shank said the prolific writer will be missed.

"He was consummate author, creating the modern-day thriller, and was one of the most visionary storytellers of our time," Shank said in a statement released Wednesday.

Four of Clancy's novels were adapted for the big screen, with Hollywood stars Alec Baldwin, Harrison Ford and Ben Affleck all taking turns playing Clancy's CIA hero "Jack Ryan.”

A fifth "Jack Ryan" movie is set for release later this year, starring Chris Pine as Ryan and Keira Knightley as Ryan's wife.

Clancy's books also served as inspiration for a series of video games released by Red Storm Entertainment – a games developer Clancy helped establish -- including "Tom Clancy's Ghost Recon: Future Soldier," "Tom Clancy's Splinter Cell: Conviction" and "Tom Clancy's Splinter Cell: Double Agent."

Clancy, who was born in Baltimore on April 12, 1947, studied English at Loyola College after a brief stint studying physics. Although he once said he wasn't smart enough to study science, Clancy won praise for his books that contained lots of scientific data and military details.

After college Clancy married his first wife, Wanda, and began working as an insurance agent, all the while collecting ideas for his future books.

He said boredom with his day job led him to try writing fiction.

Clancy remained a resident of Maryland, and in 1993 became part-owner of the Baltimore Orioles baseball team.

The writer's 17th novel, "Command Authority," is scheduled for release on Dec. 3.

With files from The Associated Press