Way to go, Gavrilo Princip. The Serb nationalist gets the distinct privilege of being remembered not as the man who simply assassinated Austrian Archduke Francis Ferdinand (and his wife) in 1914, but rather for what came of the plot: a dead Archduke and a battle between Austria and Serbia that incited World War I.
What's more, Princip was only able to kill the Archduke after a previous attempt — by one of his two cohorts — on the royal's life earlier the same day. After a hand grenade thrown at a motorcade failed to kill Ferdinand — which was the original plot — Princip went to lunch, and the Archduke decided to visit the hospital housing the grenade's victims. As fate would have it, the two again crossed paths, and the rest is history. Very violent, world-shattering history.