Maitreya, an ancient sage in Hinduism, was renowned as a prominent jnani (scholar) and parama bhakta (an inspired devotee) of Bhagavan Sri Krishna. He had studied Vedas (Shrutis), Vedangas and Dharmashastras (Smritis) systematically under the guidance of Sage Parasara.
Maitreya was an inspired devotee (anuragi bhakta) of Bhagwan. He was always in a state of ecstasy. He was not only a contemporary of Sage Vyasa but also a satirthya (a fellow religious student) of Parasara.
Maitreya was one of the advisors present in court of Yudhisthira in the Mahabharata. He had once requested Duryodhana and Dhritarashtra to be on good terms with the Pandavas, and also cursed Duryodhana for neglecting his advice. The entire Vishnu Purana is a conversation between Parasara and Maitreya, who was the srota (listener) in this conversation. The knowledge gained thus from Parasara was used by him to answer the questions of Vidura as narrated in Bhagavata Purana.
Maitreya was in Haridwar when Vidura approached him for an answer to some questions. Maitreya was instructed by Krishna to preach self knowledge (atma tattva) to Vidura on this request. The teachings are found in the third and fourth skandha of Bhagavata in 55 cantos.