Ivan was known to get very angry at times. His behaviour seems to have varied a lot, as he could at times be intelligent and quiet. His mental health became worse in the second half of his reign, especially after the death of his first wife Anastasia in 1560. It is believed that during one of his rages he caused the death of his son and heir Ivan as well as the same son's unborn son. His other son Feodor would be the next Tsar. Feodor was a weak ruler, and this led to a war called the Time of Troubles.