WHO WAS DEVADATTA?

Devadatta was the cousin and brother-in-law of the Buddha, and brother of Ananda, the Buddha's closest disciple and personal attendant. 

Devadatta is said to have parted from the Buddha's Sangha with a large number of other monks, most of whom are said to have been Shakya clan relatives of both Devadatta and the Buddha.  Devadatta wanted to form a new, more rigorous Sangha.

According to the Pāli Canon, Devadatta wanted his Sangha to adopt five additional rules or tapas (literally, austerities):

1.that monks should dwell all their lives in the forest,
2.that they should accept no invitations to meals and should live entirely on alms obtained by begging,
3.that they should wear only robes made of discarded rags and accept no robes from the laity,
4.that they should dwell at the foot of a tree and not under a roof,
5.that they should abstain completely from fish and flesh.

The Buddha allowed Devadatta's followers, still Buddhist monks, to practice all of these new austerities, except, if they wished, the last one.  He said, however, that all of the additional rules were voluntary, not compulsory.

The Buddha's not making the added rules mandatory proved a way for Devadatta to gain more supporters and followers.  For example, newer monks who did not know the Dharma well were encouraged by Devadatta to leave the Buddha and accepted him as their new leader.  After, however, the Buddha's chief disciples Sariputta and Maudgalyayana explained the Dharma to them, they went back to the Buddha.