Nanda, or Nandagopa, was the foster father of Bhagavan Sri Krishna. There is an incident mentioned in the Puranas in which Nanda Gopa is rescued by Sri Krishna from the mouth of a snake.
One day the Gopas headed by their chief Nanda performed Maheswara Puja in a nearby forest. They then decided to spend the night on the banks of Kalindi River. They were singing bhajans and keeping vigil.
Suddenly a python emerged from the forest and began swallowing Nandagopa.
The Gopas tried hard to loosen the grip of python on Nandagopa. However, they could not.
Bhagavan Sri Krishna reached the spot and gave the python a kick. It suddenly transformed into a deva, celestial being.
The Deva was known as Sudarshana. He was converted into a python due to a curse by Sage Angiras.
With Bhagavan touching him, he got relieved of the curse and attained his former form.