In Victor Hugo's novel The Man Who Laughs, King James II of England killed a nobleman and sentenced his young son, Gwynplaine, to surgical disfigurement so that he would always bear the marks of a grin. This novel inspired the 1928 silent film of the same name, starring Conrad Veidt as the mutilated Gwynplaine. This horrifying image of Veidt would inspire comic book artist Bob Kane to create the Joker, a man mutilated both inside and out.
The Joker is 1 of 10 famous cartoon characters based on real life people. You can read about the rest at Top Tenz.
-via The Presurfer