The former Marine overhauled - and, supporters say, helped save - the FBI after the 9/11 attacks. Then he took on Trump in the probe of a lifetime.

Long before the Mueller report, Robert Mueller served as a Marine in Vietnam, prosecuted John Gotti and overhauled the FBI.

The former Marine overhauled - and, supporters say, helped save - the FBI after the 9/11 attacks. Then he took on Trump in the probe of a lifetime.