Joanna of Castile
History has given this queen the sobriquet of Juana la Loca or "Joanna the Mad." But many question today whether she was really insane. Joanna married Phillip the Handsome (he fared better with the titles, obviously) in 1496. She was deeply in love with him, but he had numerous mistresses, and Joanna was jealous [source: Encyclopedia Britannica]. Her succession to the throne was murky. She became regent (temporary ruler) of Castile after the death of her mother Isabella I in 1504, but her father, Ferdinand II of Aragon, didn't accept this and convinced the courts that she was too ill to reign. Civil war in Castile made him change his tune, and although his son-in-law Phillip initially agreed that Joanna was mad and unable to rule, Phillip reneged as soon as Ferdinand left for Aragon [source: Andrean].
The courts recognized the couple as rulers, but after Phillip died, Ferdinand II returned and became regent, although not with Joanna's consent. She traveled through Granada for eight months with her husband's coffin and was rumored to kiss and caress the corpse. Her father confined her to a convent, where she stayed through his death and the reign of her son Charles I over both Castile and Aragon -- a period of 50 years [sources: Gomez et al., Andrean]. She may have had melancholia, schizophrenia or depression. But it's also possible that she wasn't insane at all. Instead, her father and son successfully perpetuated the idea to keep her from ruling [source: Gomez et al.].