On Persian King, Cambyses the Second, Killing His Brother, Bardiya, Simply Because He Had a Premonition that Bardya Would Someday Be Sitting On His Throne, and Then Killing One of His Sisters Who Had the Audacity to Show Her Slain Brother Some Sympathy - https://www.youtube.com/watch?v=KIh1v7MiyVM

Yeah, the guy was clearly insane (it's also rumored that he buried folks alive for the most minuscule of slights) and what's really bizarre is that his father, Cyrus the Great, was actually a fairly benevolent fellow (his treatment of civilians in the conquered lands of Lydia and Babylon were extremely lenient, given the time). Oh well, regression to the mean, perhaps.