Brian Williams certainly not the first to exagerate or out and out lie about his "combat" experience:

http://www.salon.com/2015/02/07/ronald_reagans_wartime_lies_the_president_had_quite_a_brian_williams_problem/

Does this change your perception of Ronald Reagan or Brian Williams? It is a little known fact that Combat hardened Marines booed John Wayne off the stage, when he showed up at some moral boosting USO tour in the South Pacific, during late 43-early 44, during WWII. Unlike Combat vets Jimmy Stewart, Eddie Albert (Tarawa), Lee Marvin (Saipan), Peter Fonda, or Clark Gable, (and of course Audie Murphy), or many Baseball Star Athletes, like Joe Dimaggio, all of these men put their careers and making money aside to serve during WWII, John Wayne never served in the Armed Forces during WWII although he was apparently physically capable. While many of his fellow actors, sacrificed John Wayne cashed in:
From: http://www.straightdope.com/columns/read/1055/was-john-wayne-a-draft-dodger
Cecil replies:

John Wayne, draft dodger? Oh, what delicious (if cheap) irony! But that judgment is a little harsh. As Garry Wills tells the story in his book John Wayne's America: The Politics of Celebrity (1997), the Duke faced a tough choice at the outset of World War II. If he wimped out, don't be so sure a lot of us wouldn't have done the same.

At the time of Pearl Harbor, Wayne was 34 years old. His marriage was on the rocks but he still had four kids to support. His career was taking off, in large part on the strength of his work in the classic western Stagecoach (1939). But he wasn't rich. Should he chuck it all and enlist? Many of Hollywood's big names, such as Henry Fonda, Jimmy Stewart, and Clark Gable, did just that. (Fonda, Wills points out, was 37 at the time and had a wife and three kids.) But these were established stars. Wayne knew that if he took a few years off for military service, there was a good chance that by the time he got back he'd be over the hill.

Besides, he specialized in the kind of movies a nation at war wanted to see, in which a rugged American hero overcame great odds. Recognizing that Hollywood was an important part of the war effort, Washington had told California draft boards to go easy on actors. Perhaps rationalizing that he could do more good at home, Wayne obtained 3-A status, "deferred for [family] dependency reasons." He told friends he'd enlist after he made just one or two more movies.

The real question is why he never did so. Wayne cranked out thirteen movies during the war, many with war-related themes. Most of the films were enormously successful and within a short time the Duke was one of America's most popular stars. His bankability now firmly established, he could have joined the military, secure in the knowledge that Hollywood would welcome him back later. He even made a half-hearted effort to sign up, sending in the paperwork to enlist in the naval photography unit commanded by a good friend, director John Ford.

But he didn't follow through. Nobody really knows why; Wayne didn't like to talk about it. A guy who prided himself on doing his own stunts, he doesn't seem to have lacked physical courage. One suspects he just found it was a lot more fun being a Hollywood hero than the real kind. Many movie star-soldiers had enlisted in the first flush of patriotism after Pearl Harbor. As the war ground on, slogging it out in the trenches seemed a lot less exciting. The movies, on the other hand, had put Wayne well on the way to becoming a legend. "Wayne increasingly came to embody the American fighting man," Wills writes. In late 1943 and early 1944 he entertained the troops in the Pacific theater as part of a USO tour. An intelligence bigshot asked him to give his impression of Douglas MacArthur. He was fawned over by the press when he got back. Meanwhile, he was having a torrid affair with a beautiful Mexican woman. How could military service compare with that?

In 1944, Wayne received a 2-A classification, "deferred in support of [the] national … interest." A month later the Selective Service decided to revoke many previous deferments and reclassified him 1-A. But Wayne's studio appealed and got his 2-A status reinstated until after the war ended.

People who knew Wayne say he felt bad about not having served. (During the war he'd gotten into a few fights with servicemen who wondered why he wasn't in uniform.) Some think his guilty conscience was one reason he became such a superpatriot later. The fact remains that the man who came to symbolize American patriotism and pride had a chance to do more than just act the part, and he let it pass.

— Cecil Adams