Durvasa Maharshi is mentioned in twenty-four separate chapters in the Mahabharata (not counting in the table of contents). He was an Avatar of Shiva as directly confirmed by Shiva Himself. Durvasa is known as a wrathful wandering Brahmana ascetic of rigid vows, fully acquainted with Ultimate Reality and all the mysteries of Dharma, and able to foresee the future, but wrath-prone as an expression of Shiva’s Lila. Sometimes in his wanderings he visited and spent some time in the assembly hall of Brahma himself, in Brahmaloka, attending upon Brahma. But generally he is described as most frequenting the Western lands of India.
The first and probably most important role that he plays is that he visited the home of Kunti aka Pritha during her childhood and she attended upon him with the most meticulously perfect hospitality, despite being terrified of him due to his reputation for cursing people for the slightest accidental missteps. In reward, he gave her a secret Mantra that could summon any Deva she chose and cause them to conceive a child with her. This is what led to the birth of the five Pandava brothers, the main protagonists of the Mahabharata.
It is mentioned that Durvasa once gave a boon to Vishnu, and the place where this occurred was a Tirtha named Varadana after this incident. This was somewhere on the northwest coast of India.
In the Mahabharata Durvasa also performed a great Yagnya for Raja Svetaki as the head priest.
At one point, during the Pandavas’ exile in the forest, Durvasa came to Hastinapura together with ten thousand disciples. Duryodhana gave them good hospitality, making arrangements to feed all ten thousand of them. Then Duryodhana convinced them to go and visit the Pandavas in the forest, knowing they would not be able to feed so many guests, and hoping they would thus incite Durvasa’s infamous wrath.
Durvasa and his followers did indeed visit the Pandavas. In order to feed them, Draupadi invoked and prayed to Krishna, who instantly teleported from Dvaraka to her side, and fed Krishna the single bite of food which she had available at that moment. Miraculously, when Krishna ate this one bite of food, Durvasa and all his followers found that their stomachs became full, and they all departed.
Once Durvasa visited a great sage named Mudgala who lived in Kurukshetra. Durvasa repeatedly tested Mudgala’s patience and spiritual state. Mudgala passed all Durvasa’s tests and won great spiritual reward.
For some time Durvasa stayed as a guest in the house of Krishna himself, where he greatly tested Krishna, Rukmini and other members of their household, yet they proved themselves admirable hosts. Krishna Himself explicitly attests to Durvasa’s Divinity.
After the Kurukshetra war, Durvasa came and visited the dying Bhishma on the battlefield, and listened to his last discourse.