Sima Yu
When Sima Yu was four years old, there was a fire in the palace, and Emperor Wu walked up a tower to observe it. Sima Yu pulled him aside and said, "At night, when something unusual like this happens, we should take precautions. The light of the fire should not shine on the emperor." Emperor Wu was surprised by this perceptive observation by a child, and praised the young prince as very much like his own grandfather Sima Yi. This was part of the reason why Emperor Wu let Crown Prince Zhong remain his heir. In 289, he created Prince Yu the Prince of Guangling. After Emperor Wu died in 290, Crown Prince Zhong ascended the throne as Emperor Hui, and Prince Yu was created crown prince.