The Serenity Prayer is perhaps the most famous prayer in the world and the cornerstone of A.A. Almost everyone has heard it or read it:
God grant me the serenity to
Accept the things I cannot change
The courage to change the things I can
And the wisdom to know the difference
The prayer is sometimes attributed to St. Anthony or is said to have its origins with the Greek Stoics. Actually, it was written in 1943 as a kind of sermon note by a famous professor, theologian and preacher by the name of Reinhold Niebuhr.
Niebuhr was a professor at the Union Theological Seminary in New York City and he was very influential in the years between WW I and WWII and in several decades after in the long struggle for social justice for labor, for blacks, for Jews, and in rousing an isolationist nation to war against Hitler and Mussolini.
This is the prayer as originally written by Niebuhr:
God grant us the grace to
Accept with serenity that which we cannot change
The courage to change what should be changed
And the wisdom to distinguish the one from the other