Sima Gan (司马榦; 232 - 26 February 311), courtesy name Ziliang (子良),(平原王干，字子良。) Jin Shu, vol.38 was the youngest son of Sima Yi and his main wife Zhang Chunhua, and a younger brother of Sima Shi and Sima Zhao. Sima Yi, Sima Shi and Sima Zhao eventually became regents of the Cao Wei state during the Three Kingdoms era.

Life under Cao Wei Sima Gan was born in 232 during the reign of Cao Rui, as the youngest son of Sima Yi and his wife Zhang Chunhua. Like his brothers, Sima Gan was given various posts and titles during the Cao Wei era; unlike them, Gan's posts and titles were largely minor or ceremonial.(少以公子魏时封安阳亭侯，稍迁抚军中郎将，进爵平阳乡侯.) Jin Shu, vol.38

The first recorded historical event Sima Gan was involved in was the attempted coup by Cao Mao, by then a puppet under Sima Zhao's control. In June 260, Cao Mao launched a coup in an attempt to seize back power from Sima Zhao. Man Changwu (a grandson of Man Chong) was in charge of guarding one of the palace gates. Sima Gan led his men to the palace to assist Sima Zhao, but Man Changwu refused to let him pass and told him to enter through another gate instead. Later, when Sima Zhao asked Sima Gan why he was late, Sima Gan told him what happened.(高貴鄉公之難，以掾守閶闔掖門，司馬文王弟安陽亭侯幹欲入。 ... 長武謂幹曰：「此門近，公且來，無有入者，可從東掖門。」幹遂從之。文王問幹入何遲，幹言其故。) Shiyu annotation in Sanguozhi vol. 26.

Sima Zhao was made Prince of Jin on 2 May 264.(咸熙元年春...三月...己卯，进晋公爵为王，...) Sanguozhi, vol.04 With this elevation, when Sima Zhao established the Five Feudal Ranks of Zhou, Sima Gan was made Count of Dingtao.(五等建，改封定陶伯。) Jin Shu, vol.38

During the Jin era Sima Zhao died in September 265, and was succeeded as regent of Cao Wei by his son Sima Yan. In February 266, Sima Yan accepted Cao Huan's abdication and founded the Jin dynasty. Sima Gan was then made Prince of Pingyuan, with a fiefdom of 11,300 households. Although his fiefdom was large, he did not take an active role in administration; instead, he appointed officials based on their abilities and the positions which needed to be filled. He also allowed his income (cloth, silk) to accumulate and rot.(武帝践阼，封平原王，邑万一千三百户，给鼓吹、驸马二匹，加侍中之服。.....干虽王大国，不事其务，有所调补，必以才能。虽有爵禄，若不在己，秩奉布帛，皆露积腐烂。) Jin Shu, vol.38

Sima Yan died in May 290, and his son Sima Zhong ascended the throne. During audiences with the emperor, as the emperor's great-uncle, Sima Gan was allowed to wear his shoes and carry his sword, as well as walk at a normal pace.(惠帝即位，进左光禄大夫，侍中如故，剑履上殿，入朝不趋。) Jin Shu, vol.38

The Book of Jin recorded several anecdotes between Sima Gan and his grandnephew Sima Jiong. During the War of the Eight Princes, after Sima Jiong defeated Sima Lun, while other clansmen of the Sima family and court officials sent oxen and wine as gifts to Sima Jiong, Sima Gan offered him 100 cash. At their meeting, Sima Gan said, "The Prince of Zhao (Sima Lun) caused a rebellion and you managed to put it down; that is your credit. Now, I'm congratulating you using these 100 cash. Even so, it is very difficult to remain at a high position; you must be careful and cautious." After becoming regent, Sima Jiong once received a visit from his great-uncle. While Sima Jiong stepped out of the house and received Sima Gan with courtesy, upon entering the house, Sima Gan sat down on Jiong's bed and did not allow Jiong to be seated. Gan then said, "You must not emulate the son of that Bai woman (referring to Sima Lun)." After Sima Jiong was killed in January 303, Sima Gan cried bitterly and told those around him, "The Sima clan is waning; only this child is the most capable. Now that he has died, the Sima clan is in peril!"(齐王冏之平赵王伦也，宗室朝士皆以牛酒劳冏，干独怀百钱，见冏乂之，曰：“赵王逆乱，汝能义举，是汝之功，今以百钱贺汝。虽然，大势难居，不可不慎。”冏既辅政，干诣之，冏出迎拜。干入，踞其床，不命冏坐，语之曰：“汝勿效白女儿。”其意指伦也。及冏诛，干哭之恸，谓左右曰：“宗室日衰，唯此儿最可，而复害之，从今殆矣！” ) Jin Shu, vol.38

After Sima Yue became Emperor Hui's last regent in 306, he decided to pay Sima Gan a visit at Gan's residence in Luoyang. Gan declined to meet him; after a lengthy wait, Gan despatched a servant to see Yue off. At the same time, Gan left the door ajar, allowing him to observe the scene from behind the door. At the time, people could not understand his actions; they thought that Gan was ill, or that he had turned reclusive.(东海王越兴义，至洛阳，往视干，干闭门不通。越驻车良久，干乃使人谢遣，而自于门间窥之。当时莫能测其意，或谓之有疾，或以为晦迹焉。) Jin Shu, vol.38

Descendants Sima Gan was recorded to have two sons. The elder Sima Guang died young and presumably left no descendants. The younger Sima Yong was made Duke of Ande County in 290; he and his family were later killed, presumably during the Disaster of Yongjia.(有二子，世子广早卒，次子永以太熙中封安德县公，散骑常侍，皆为善士。遇难，合门堙灭。) Jin Shu, vol.38 Notes

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