Devadatta was the son of Suppabuddha who was the maternal uncle of the Buddha, was jealous of him since his early days.
When the Buddha went to visit the Kapilavatthu and speak among the Sakyan nobles, many dignified men joined the Sangha. That was the time when Devadatta, also had, joined the Sangha; and in that same period of time he, too, developed some extreme supernatural powers. However, on the other hand, his opposition and jealousy against the Buddha never reduced.
One day, when he went to Ajatasattu who was the future ruler of the Magadha Janapada he amazed him by a unbelievable appearance. There, he appeared in his knees as a kid having snake strap. Fascinated and impressed by the wonder Ajatasattu became his follower and his big fan.
Back to the order, Devadatta, one day declare his power over the Buddha to suppose the leadership of the Order by arguing that the latter was old and senile. His argue, however, did not suggest much response in the order. So, he complaint against both - the Buddha and the Order.
Dissatisfied by this, he then went to Magadha and instigated prince Ajatasattu to resort to fratricide by killing Bimbisara and take over the throne, chiefly because Bimbisara was the chief patron of the Buddhist order, and his removal would mean the loss of royal support to the order. The scheme, however, did not work out originally at first. So, he employed sixteen archers to kill the Buddha. But the archers in turn became the followers of the Buddha.
Irritated by this, Devadatta himself then tried to kill the Buddha by throwing down a great rock from a peak of the mount Gijjhakuta when the latter was walking down the slopes. The Buddha, however, escaped because two peaks appeared from the ground and arrested the advancement of the rolling rock.
In additional, irritated and disturbed, Devadatta then won over the royal elephant-keepers to let loose a violent elephant Nalgiri, also called Dhanapala, on the path of the Buddha by making him drunk with toddy. Thus Nalgiri was let loose. The violent and dangerous looking drunk elephant when walked on the streets the people run off at his sight. Yet, the Buddha kept on walking in his usual dignity and calm, though, Ananda tried to avoid and protect him. In the same moment, a frightened woman running helter-skelter dropped her baby on the feet of the Buddha. When the animal was just about to stamp on the baby the Buddha in his usual equipoise touched the animal’s forehead and pat it gently. Calmed by the Buddha’s patting the elephant bowed down before him on his knees. The people, further, noticed that the Buddha delivered a talk on dhamma to the elephant.
The tradition believes that had the elephant not been a beast he would certainly have become a Sotapanna which was the first step to the Arahatahood after having listened to the talk.
The Nalgiri elephant-episode, however, made Devadatta very hated and he had to run away from the city. Moreover, the royal favour , which he had enjoyed so far, was also calm down to honour the public opinion.