John Wilkes Booth was a stage actor and Confederate sympathizer during the American Civil War. Booth plotted to kill President Abraham Lincoln as well as Secretary of State William H. Seward and Vice President Andrew Johnson with the help of conspirators Lewis Powell and George Atzerodt.
In the Timeless Universe
In the original timeline, Booth assassinates Abraham Lincoln in Ford's Theatre on April 14, 1865 by shooting him in the back of the head. After killing Lincoln, he stabs Major Henry Rathbone, injuring him. He then jumps off the balcony from which Lincoln had been viewing the play thus injuring his leg, and shouts to the audience before escaping.
In the altered timeline, Garcia Flynn arms the conspirators with modern handguns to perform their assassinations. Booth, however, does not want to use the new gun calling it 'ugly' and would prefer to use his derringer and knife for dramatic effect. Flynn warns Booth that he'll need more than the one bullet his derringer will provide because he must also assassinate Ulysses S. Grant, but Booth still refuses to use the modern gun. Booth's refusal to cooperate causes Flynn to knock Booth out and perform the assassinations himself. Booth was said to have later been hunted down and killed.
John Wilkes Booth at Wikipedia