shlokam:

With protection and boon giving posture of hands, with axe and deer, wearing moon, snakes, yellow robe, Three eyed, Auspicious, Dark-blue throated, that Divine riding the bull, Remover of the poison, Colorful (peacock) feather like formed (I salute).

purANa of the deity

nIla kaNThar: black (blue) throated Lord

Demons and gods wanted to have the amR^ita the nectar that would make one live long avoiding death. The amR^ita was in the milky ocean and required churning the huge ocean to get out the nectar. They came together to collectively churn the big ocean. They churned the milk ocean with ma.ndhAra mountain as the stem and serpentvAsuki as the rope. In the process, due to the pain serpent vAsuki emitted the poison hAla (meaning destructive). At the same time one more poison came from the ocean hAla. Both put together became an disastrous poison that threatened the very existence of all including the divines, deamons and the other lives. mahA vishNutried to stop that. His body turned blue, but he couldn't stop it. Terrified by the destroying power of the poison, all of them surrendered to Lord Shiva, the Giver of Refuge. (So far they had never thought of Lord shiva to offer first the amR^ita, but only when it came to disaster they remembered God !)

The Graceful God took the hAlAhalam as if it is a fruit in the hand. Asked all of them, what He should do with that. They pleaded that the poison would annihilate them all if He left it off. Lord smilingly put it into His mouth ! But isn't all the worlds very much inside the God ? Though it will not affect the Lord, but the worlds would be again affected by the poison, Goddess Shakthi, the mother of all creatures, stopped the poison in His throat by putting her hand in His throat. The poison stayed there as a small black (blue) stain. Hence the Lord is called nIlakaNThar .

Now with the blessings of God, the divines continued to churn the ocean and got the amR^ita. God gave the amR^ita to the divines, but had only the poison. For the Lord, Who remains Eternal even after the divines who ate the amR^ita die, what is the need for amR^ita ? He is the greatest amR^ita one can seek!

See Also: 
1. Pradosham

2. Neelakanda Vijaya

வடங்கெழு மலைமத் தாக 
 வானவர் அசுர ரோடு
கடைந்திட எழுந்த நஞ்சங் 
 கண்டுபல் தேவ ரஞ்சி
அடைந்துநும் சரண மென்ன 
 அருள்பெரி துடைய ராகித்
தடங்கடல் நஞ்சம் உண்டார் 
 சாய்க்காடு மேவி னாரே.  4.65 2

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