Mahabharata is essentially the story of the Kauravas and
Pandavas. Krishna’s story is just a part of the narrative and dealt
exhaustively in the Harivamsa. So when did Krishna make an entry in the
Mahabharata.
Bhagavan Sri Krishna appears in the story of Mahabharata
soon after Draupadi married the Pandavas.
A stranger comes into the house of the Pandavas and
introduces himself as Krishna, Kunti’s nephew, her brother Vasudeva’s son.
Sri Krishna is immediately included as part of the family.
Krishna also counseled Kunti and Pandavas to return to
Hastinapur. Duryodhana and the others on the side of the Kauravas cannot ignore
the Pandavas who had married the daughter of the mighty Durpada, the King of Panchala.
From this point onwards, Krishna is the chief advisor,
negotiator and messenger of the Pandavas.