Mary Tudor is confirmed to have actually existed and I’m not surprised that she’s believed to be the origin of the Bloody Mary legend as her life was often soaked in blood. Mary Tudor was the daughter of the notorious King Henry the VIII who is famous for putting his wives to death whenever he grew tired of them. So, she did see her share of "bloody" acts because Mary was the daughter to the very first wife of King Henry.
Not only did King Henry kill people, but he disowned Mary, and forced her to work as a servant for her younger sister. Well at the age of 37, Mary became queen, so she finally had a chance to turn things around. Unfortunately, she didn't really change much, except for the fact that she didn't kill husband after husband; she did burn people at the stake because they didn't follow her religion. So, that is where the name "bloody mary" came from.