Contemporary sources present disparate accounts of Ivan's complex personality. He was described as intelligent and devout but also prone to paranoia, rage, and episodic outbreaks of mental instability that increased with age.[6][7][8] In one fit of anger, he murdered his eldest son and heir, Ivan Ivanovich, and he might also have caused the miscarriage of the latter's unborn child. This left his younger son, the politically ineffectual Feodor Ivanovich, to inherit the throne, a man whose rule and subsequent childless death directly led to the end of the Rurikid dynasty and the beginning of the Time of Troubles.