Tom Clancy, a prolific writer famous for his best sellers about espionage and the military, died Oct. 1 at the age of 66, ABC News has confirmed with his publisher, Penguin Group.

The cause of death is unknown.

'I'm deeply saddened by Tom's passing. He was a consummate author, creating the modern-day thriller, and was one of the most visionary storytellers of our time,' Penguin Group executive David Shanks said in a statement. 'I will miss him dearly and he will be missed by tens of millions of readers worldwide.'

Clancy, a Baltimore native who joined R.O.T.C. in college but had to drop out because of his poor eyesight, worked at an insurance agency before turning his passion -- writing -- into a full-time job. He published his first book, 'The Hunt for Red October,' in 1984. The novel was later turned into a film, starring Alec Baldwin and Sean Connery. Several of Clancy's books were turned into movies.

According to Clancy, this was the job he was always meant to do.

In Memoriam Photos: Tom Clancy

As a child, ''I never read kids' books,'' he told New York Times magazine in 1988. ''At least not the usual kids' books. I remember reading Jules Verne in the third grade. I started on Samuel Eliot Morrison in the fourth or fifth grade - he started me on military history. I read a lot of science fiction. I rea.