When Morgan Freeman steps in front of the camera, you watch him, you care about what he's doing.

"He is a man of real substance," says Ben Affleck who’s co-starring with Freeman in Tom Clancy’s psychological spy thriller, "The Sum of All Fears" which opens May 31.

Affleck is playing Clancy's famous CIA hero Jack Ryan (previously played by Alec Baldwin and Harrison Ford).

"I knew he would bring weight and integrity to the movie," Affleck says, "and selfishly it was a thrill to work with him."

In certain circumstances, Affleck's testimonial would sound like just so much flattery, but his description seems to fit Morgan Freeman to a tee. In fact, the Academy Award©-nominated actor is one of those rare individuals who is difficult to over-praise. Throughout Freeman’s career the actor has displayed remarkable versatility, from the frighteningly charismatic pimp he portrayed in "Street Smart," to the genteel and patient chauffeur in "Driving Miss Daisy," to the troubled President of the United States in the disaster film "Deep Impact," Freeman seems incapable of striking a false note.

In "The Sum of All Fears," he brings an intellectual gravity to the role of CIA director William Cabot. At the center of the movie, his character lends an air of authenticity to the story. By contrast, in his real life, Freeman is an easygoing person with a natural sense of humor and a kind of shyness that is remarkably common among actors who only seem to feel comfortable exhibiting their full range of emotions in front of a camera or on a stage.

Not one of those actors who likes to chew over the fine points of his craft, Freeman simply enjoys making it all look effortless. "Unless I'm playing someone who really lived, I don't do research," Freeman says. "I just create it. Well…create is not the right word since the writer has done that for you. What I do is perhaps decide on certain physical properties of the character that haven't been delineated. For example, for this role I gained some weight to give the character more of a presence that I felt a CIA director would have."

Freeman adds after recent events, it's difficult not to take Clancy's premise -- that rogue terrorists could smuggle a weapon of mass destruction into the United States -- to heart.

"For all the high tech gadgetry on which the government spends billions of dollars every year," Freeman says, "this low-tech approach to mass destruction was frighteningly realistic."