If you spend any time on Facebook, you've probably noticed many people have changed their profile pictures to that of a celebrity they resemble. While the word "doppelganger" has come to mean someone with similar physical features, originally it was a ghostly double and a bad omen. Abraham Lincoln is said to have seen his doppelganger on the night he was first elected President, and Mary Todd Lincoln suggested it meant he would be re-elected to a second term but not survive.