Sima Shi
Cao Fang was very angry about the deaths of Li Feng and Zhang Ji, and later in 254, his associates submitted a plan to him—that when Sima Shi's brother Sima Zhao would arrive at the palace for an official visit before heading to his defense post at Chang'an, to kill Sima Zhao and seize his troops, and to then use those troops to attack Sima Shi. Cao Fang was apprehensive and paralysed, and did not implement the plan, but news was still leaked to Sima Shi. Sima Shi then forced Cao Fang to step down, although Sima Shi spared his life and gave him his old title of Prince of Qi. When Sima Shi notified Cao Fang's stepmother, Empress Dowager Guo, that he intended to make Cao Pi's brother Cao Ju, the Prince of Pengcheng, emperor, she managed to persuade him that such a succession would be improper—that since Cao Ju was the uncle of her husband, Cao Rui, such a succession would leave Cao Rui effectively sonless with no heir. Sima Shi was forced to agree with her, and he made, as she suggested, Cao Mao emperor instead. Cao Mao, although 14 years old at the time, was known for his intelligence, and Empress Dowager Guo might have believed that he, alone of the princes and dukes, might have had a chance of counteracting the Simas.