House Targaryen carries the trait for insanity in its bloodline. Over three hundred years of heavy inbreeding, marrying brother to sister whenever possible to "keep the bloodline pure," resulted in many of the medical problems seen with incest, particularly mental instability. The most prominent example of the Targaryen madness was the last Targaryen king, Aerys II, who subsequently became known as "the Mad King". Aerys suffered from some sort of paranoid schizophrenia, hearing voices in his head that weren't real and told him to burn people alive because they were all plotting against him.