Praised as the Lila Avatar, Bhagwan Vishnu takes different avatars to protect the goodness of the world whenever it is threatened or challenged by opposed forces. Apart from the Dasavataras, he also took varied avatars which were needed to eliminate few demonic forces who could be destroyed with specific conditions. One such avatar where Bhagwan Vishnu took the twin forms was the Nar and the Narayan Avatar.
The Bhagavat Puran mentions this divine Avatar of Bhagwan Vishnu taken up for the preservation of Dharma. The Nar Narayan in the form of twins, represent the Nar (Human form) and the Narayan (Divine form), but with one soul. They are prominently worshipped in Badrinath temple as the twin pair of Bhagwan Vishnu. The reason behind Bhagwan Vishnu taking this avatar was to kill the demon Sahasra Kavach.
Sahasra Kavach was a demon who had thousand armours attached to him given as a boon by Brahma Ji. He was unconquerable by anyone due to the protection of his armours and tormented the worlds with his power. When all sought refuge in Bhagwan Vishnu to protect them, he divided his form into the twin pair of Nar and Narayan and was they were born as the sons of Brahma.
Nar and Narayan started observing great penance to obtain strength to defeat Sahasra Kavach. Sahasra Kavach came to know about this and challenged them for battle. Nar and Narayan decided to take turns in fighting him. While one fought with the demon, the other observed penance to gain strength during that time. In this way, for every five hundred years, they started breaking his armour one by one. Finally Sahasra Kavach was left with only one armour.
When it was the turn of Nar to break the final armour of Sahasra Kavach and destroy him, the demon fearing for his life, went and hid in the shadows of the Sun God, and came to be seen nowhere. Later he transformed his soul into the Sun God, and was born as his son, who was none other than Karn of the Mahabharat. To finish the final battle with Sahasra Kavach, Nar was born as the third Pandav Arjun and Narayan was none other than Shri Krishna. In the final war of the Mahabharat, Arjun kills Karn and finally puts an end to their long battle with Sahasra Kavach. It was for this very reason that Shri Krishna and Arjun were never separable and Shri Krishna treated him as his own entity.
Nar and Narayan are representations of both intelligence and power put in two forms, but a unified soul. They teach us that power when power is combined with intelligence and both are used for upholding Dharma, they become divine entities to be worshipped and revered by the entire world.