Introduction
Takshaka is a king of the Nagas, the serpent race, and one of the sons of Kadru named in the Mahabharata's genealogies. He is best known for killing King Parikshit, the grandson of Arjuna, which set in motion the events framing the recitation of the Mahabharata.
The curse on Parikshit
According to the Adi Parva, Parikshit, while hunting, insulted a meditating sage by hanging a dead snake around his neck. The sage's son cursed the king to die by snakebite from Takshaka within seven days. Parikshit took every precaution, but Takshaka reached him disguised, by some accounts hidden inside a fruit offered by a Brahmin, and killed him.
Janamejaya's revenge
Parikshit's son Janamejaya, on learning that Takshaka had killed his father, began the Sarpa Satra, a great sacrifice intended to destroy the entire race of serpents by drawing them into the sacrificial fire. Takshaka, warned by Indra, took refuge with him in his own court, but the ritual's power was strong enough to threaten to draw in even Indra and Takshaka together. The sacrifice was finally stopped through the intervention of the young sage Astika, whose mother Jaratkaru was a sister of Vasuki, before Takshaka could be destroyed.
The frame of the Mahabharata
It is at this sacrifice, held by Janamejaya, that the sage Vaishampayana, a student of Vyasa, is said to have first recited the whole of the Mahabharata, at Vyasa's instruction. Takshaka's act is therefore, in the epic's own telling, the reason the story came to be told at all.
Later mention
Takshaka is named again in the Bhagavata Purana and other Puranic literature among the great Naga kings, alongside Vasuki and Karkotaka.