Part of his education came from novelist Tom Clancy, who died Tuesday in a Baltimore hospital. The bestselling author of espionage tales was 66.

As a young actor, Affleck was cast in the 2002 film adaptation of "The Sum of All Fears," in which Affleck played Clancy's famous CIA operative Jack Ryan. 

“I think Tom was really the first major writer in the genre to make realism the top priority," Affleck said Tuesday.

"When you read one of his books, you had the distinct feeling that he was depicting military or espionage situations exactlyas they really are. He hews to his research religiously, and the result is an indisputable sense of authenticity.

"Other spy books feel invented, while his feel like genuine accounts of events that took place but that no one knows about. I think the movie adaptations have risen and fallen in direct proportion to how well they kept his sense of authenticity and nuts-and-bolts realism.”

Affleck added that Clancy was not as macho as his writing might have suggested.

"I spent time at his home with his family, and, despite his image as a tough guy, he was incredibly sweet and loving," the actor and director said.

"He cared a lot about the care Johns Hopkins gave children. Despite the fact that he spent so much time writing about the military and clandestine services, he thought the real heroes of the world were doctors — particularly ones who cared for children. I will miss him."

By John Horn