One story is of Wang ZongYue who was passing through Chen Jia Gou. After a conversation with the villagers, many challenged him to combat. Using his soft ‘internal’ style against their hard ‘external’ style, he beat them all. Impressed by his skill the Chen family invited him to teach them his skill.
An alternative version, preferred by the Chen family, is that a family member, Chen WangTing (1597-1664), created Taijiquan. The style was handed down strictly within the family until the arrival of Yang LuChan.
belief is that it was developed by an immortal named Chang SanFeng in the 16th Century. He was living as a hermit on Wudang Mountain and passed his art onto Chang Sung-Qi. Some believe that this system is Nei Chia than Taijiquan.