Kristen IV was one of the longest ruling emperors of the Krissen Empire and during his 70th birthday, he put to death 7 of his sons, 4 of his daughters, over 20 of his grandchildren as well as more than 4000 others he imprisoned for attempting to usurp the throne. At that time, more than 100 noble families were involved in that incident.
That was one of the most well-known incidents in the history of the Krissen Empire that caused Krissen IV to henceforth be known as the Ironheart Emperor. The reason it happened was simple: Krissen IV had been on the throne for far too long and had a ruling term of a staggering 84 years. Even the three sons of his that were made crown prince didn't live as long as he did. In the end, the few remaining sons of his who yearned to be emperor decided to send their father on a premature journey from the world, but they were exposed and dealt with in the end.