The divine serpent on whom Vishnu rests is Shesha, also called Ananta or Adishesha.
Shesha is the cosmic serpent of Hindu tradition and the king of the nagas. In familiar Vaishnava imagery, Vishnu reclines upon Shesha’s coiled body in the Ocean of Milk, while the serpent’s many hoods spread above Vishnu like a protective canopy. This form of Vishnu is often identified as Narayana.
The name Shesha comes from a Sanskrit root meaning “that which remains.” This reflects the idea that Shesha endures even after the destruction of a cosmic age. Puranic accounts also describe him as supporting the worlds and praising Vishnu with his many mouths.
Shesha is easily confused with other famous serpents. Vasuki is associated with the churning of the Ocean of Milk, Kaliya is the serpent subdued by Krishna, and Takshaka is prominent in the Mahabharata. Shesha is also linked with Vishnu’s incarnations: he is traditionally identified with Lakshmana, and in some traditions with Balarama.