Сыма Цянь
Some Tong families are said to be descendants of Sima Qian. Sima Qian was a Han Dynasty historian who wrote the Records of the Grand Historian. According to this story, when Sima Qian was put in prison by the Emperor, his children fled. His two sons decided to change their name, each using one character of the Sima surname (司马). The Si (司) was modified to Tong (同) by the addition of a stroke, while Ma (馬) was modified to Feng (馮). There remains a taboo that the two families should not intermarry.