Who assassinated President Lincoln?

John Wilkes Booth

On April 14th, 1865, President Lincoln was shot in the back of the head in Ford's Theater in Washington, D.C. The president was watching the play "Our American Cousin", written by Tom Taylor. He was shot with a .44 caliber Derringer gun. Prior to this, John Wilkes Booth had been a somewhat well-known actor.

Here is a source for further reading.

http://www.history.com/this-day-in-history/president-lincoln-dies