The devas and asuras were cousins who were always at war. Once there came a time when the cousins agreed to stop fighting and work together. The idea was to churn the ocean of milk which would yield Amrit or the nectar of immortality. Anyone who had a sip of Amrit would live forever. The cousins, devas and asuras, both wanted to become immortals. So, they agreed to churn the ocean of milk.
They placed Mandara, a large mountain, on the ocean bed. The mountain was to be used as a rod to churn Amrit out of the ocean. Lord Vishnu took the form of a giant tortoise to support Mount Mandara on the ocean bed and prevent it from sinking. The serpent king Vasuki allowed the cousins to use him as the rope to rotate the huge churning rod. The serpent was looped around Mount Mandara. Vasuki’s tail was held by the devas and his head was held by the asuras. Using all their might the cousins began to churn the ocean of milk.
To their dismay, as the ocean of milk was churned hard, it threw up a cloud of deadly poison — Haalaahala. This poisonous gas choked the devas and the asuras. But, before it could inflict severe damage, Shiva scooped it up in his hand and swallowed it. His consort, Parvati, was quick to grasp Shiva’s neck tightly to prevent the poison from going down his throat. As a result, Shiva got a blue patch on his neck, earning him the name Neela-kanta.