John Wilkes Booth

 was the actor who assassinated President Abraham Lincoln in the middle of April 1865. Both Aaron Eddowes, the would-be Lincoln assassin foiled by the fifth Doctor, and Will Johnson were known to have mentioned Booth's complicity after the fact. (TN: Blood and Hope)

Another, possibly conflicting account tells of John being killed the night before he would kill Lincoln by Robert Knox. (BFA: Assassin in the Limelight)