Sima Qian (py. si1 ma3 qian1, wg. Ssuma Ch'ien, trad. ch 司馬遷, sim. ch 司马迁) was one of the most important Chinese historiographers. His Chinese courtesy name was Zichang (trad. ch. 子長, sim. ch. 子长, py. zi3 chang2).
His father Sima Tan served in the Han Dynasty government between the periods Jianyuan (140 BC-135 BC) and Yuanfeng (110 BC-105 BC), where he held the office of the Prefect of the Grand Scribes (太史令, Tai Shi Ling, also translated "Great Historian"). Among his duties were the supervision of sacrifices and calendar, the investigation of astrological questions and the care of the Imperial Library. He also collected historical records and thereby laid the foundation for the work of his son.
Sima Qian was born in 145 or 135 BC at Longmen near present-day Hancheng, where he grew up in a rural setting. At the age of 10, he was already well versed in old writings and at 20 he set out on a major journey through the empire. He visited the reputed graves of the ancient sage kings Yu and Shun and studied in the home province of Confucius. When he came back, he served as a Palace Attendant (Lang Zhong). In 110 BC, he was sent westward on a military expedition against some "barbarian" tribes.
Also in 110, Sima Tan fell ill and could not attend the imperial Feng Sacrifice. Thinking he was going to die, he summoned his son and ordered him to carry on the family tradition and to complete the work he had begun - this at least is what Sima Qian tells us, though the exact details cannot be reconstructed.
In 107 BC, Sima Tan died and Sima Qian inherited his office. In 104, he began compiling the Shiji (史記, "Historical Records", also known as Records of the Grand Historian), his opus magnum, in which he recounted Chinese history from the time of the mythical Yellow Emperor until his time.
In 99 BC, he got involved into the Li Ling affair. Li Ling, a military officer, had led a disastrous campaign against the Xiongnu in the north and was taken captive. This aroused the wrath of Emperor Wudi and everybody at court tried to flatter him by condemning Li Ling. Only Sima Qian defended Li, who had never been his friend but whom he respected. Wudi, who perhaps was already angry at Sima because of the not very complimentary remarks about his father, Emperor Jingdi, in the Shiji, gave him the choice between execution or mutilation (i.e. castration). Sima Qian chose the latter in order to be able to complete his work.
It is not known for sure when he stopped working at the Shiji, but it seems to have been some years before his demise, either in the Taichu period (104-101 BC) or the Tianhan period (100-97 BC), though the former date would make his decision for mutilation instead of castration difficult to understand. The exact date of his death isn't known either, the most commonly given dates are 90 resp. 86 BC.
Sima Qian and his Shiji had a tremendous influence on Chinese historiography and prose, well comparable to Herodotus and his Historiai.