Billy the Kid (born William Henry McCarty, alias Henry Antrim, Kid Antrim, & William H. Bonney) has often been referred to as The Left-Handed Gun. In 1958, a movie with that title was made and starred the inimitable Paul Newman. The myth began with the publication of this ferrotype:

Billy The Kid

It seems to show that Billy is left-handed, but if you look closely, the buttons on his vest are on the wrong side, and the buckle on his belt is also reversed. This is a mirror image, and Billy the Kid was in fact right-handed.