The Leader of the Free World is an expression, primarily used during the Cold War, to describe the President of the United States. The phrase implies that the U.S. president as leader of the principle democratic superpower of the time was, by extension, the leader of all the worlds? democratic nations. Although it had a Cold War origin, it is still used.[1] In addition, the phrase is sometimes used satirically when either the president or the United States engages in behavior that other nations disagree with.
http://en.wikipedia.org/wiki/Leader_of_the_Free_World