Devadatta was the son of Suddhodana's brother Suppabuddha and thus was the Buddha's cousin. His name means `God-given'. When the Buddha returned to Kapilavatthu for the first time after his enlightenment, several young Sàkyan men, including Devadatta, decided to become monks (Vin.II,182). For some years, Devadatta proved to be a good and diligent monk and in several places in the Tipiñaka he is praised as such (A.IV,402ff; Vin.II,189). The Buddha named him together with several others as an exemplary monk (Ud.3-4). But things were to change. As a result of diligent meditation Devadatta began to manifest psychic powers and gradually became proud as a result. Later he came to feel that the Buddha was drifting too far from traditional ascetic practices and he was able to get some other monks too agreed with him.
Confronting the Buddha on this issue, Devadatta insisted that he make several practices compulsory for all monks Ý (1) that they should live only in the forest, (2) that they never accept invitations to eat at devotees' homes but live only by alms gathering, (3) that they wear only rag robes, (4) that they live in the open not in a monastery, and (5) that vegetarianism be compulsory. Devadatta's demands were refused and so he and his supporters separated from the Buddha and his disciples. This was the greatest crisis the Buddha had to face during his 45 year ministry.
The Vinaya even claims that Devadatta actually tried to murder the Buddha on two occasions, although it is not certain whether this is true or just a later attempt to make him look as bad as possible (Vin.II,190-94). There is no more information about Devadatta in the Tipiñaka itself, but tradition says his supporters eventually abandoned him to return to the Buddha and that he later died discredited and alone.