Emperor Yuan of Jin mother Xiahou Guangji
Early career
Sima Rui was born in 276 in the then Jin capital Luoyang, as the son of Sima Jin (司馬覲) the Prince of Langya and his wife Princess Xiahou Guangji (夏侯光姬). (According to an alternative account at the end of his biography in the Book of Jin, he was actually the prouct of an affair between Princess Xiahou and a minor official from the family of the Cao Wei general, Niu Jin.) His father died in 290, and he became the Prince of Langya. The Book of Jin referred to him as steady and dexterious, personality-wise.
In 304, in the midst of the War of the Eight Princes, Sima Rui participated in Sima Yue the Prince of Donghai's campaign against Sima Ying the Prince of Chengdu as a minor general.  After Sima Ying defeated Sima Yue, Sima Yue executed Sima Rui's uncle Sima Yao (司馬繇) the Prince of Dong'an, which caused Sima Rui much fear.  He decided to flee back to his principality Langxie (roughly modern Weifang, Shandong), under counsel of Sima Yue's assistant Wang Dao, whom he befriended during the campaign.  He first tried to head back to Luoyang, but when he was about to cross the Yellow River, he was stopped by guards instructed to stop any nobles or high level officials from crossing (as Sima Ying had ordered such, fearing that nobles would desert him or plot against him).  His own guard Song Dian (宋典) then arrived and gave him a shove, pretending that they were just construction workers.  The guards then allowed them to cross.  After Sima Rui got to Luoyang, he took his mother Princess Dowager Xiahou and headed to Langxie, where they spent the next few years away from the War of the Eight Princes.
In 307, Sima Yue, who had emerged victorious in the aftermaths of the War of the Eight Princes as the regent for Emperor Huai, under the advice of his wife Princess Pei, commissioned Sima Rui as the military commander of parts of Yang Province (揚州, modern Zhejiang and southern Jiangsu and Anhui) south of the Yangtze River, with his post at Jianye.  Wang Dao became his chief advisor.  As Sima Rui lacked fame, after he arrived in Jianye, few of the powerful local gentlemen would come visit and support him.  Under Wang Dao's counsel, Sima Rui personally visited He Xun (賀循) and Gu Rong (顧榮) and invited them to serve in his administration.  He and Gu were well regarded by the local population, which eventually began to trust Sima Rui's leadership.  Wang Dao and his cousin, the general Wang Dun, served in key roles, and it was said at the time that the domain was ruled equally by the Simas and the Wangs.
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