Leonardo da Vinci
Leonardo da Vinci, one of the most brilliant men in history, took his sinistrism to an extreme: he wrote from right to left. Historians have plenty of creative theories to explain this so-called "mirror writing" — named because you had to hold it up to a glass to read it. For example: perhaps he was trying to make it harder for people to sneak a peek at his notes and lift his ideas. One argument, however, is less fanciful but perhaps more logical: writing in ink from left to right was too messy because Leonardo was a southpaw. Some historians have suggested that da Vinci's left-handedness added to his genius, because it forced him to think and see in an extraordinary way. (If so, he wasn't alone: fellow left-handers include rival Renaissance titans Michelangelo and Raphael.)