As mentioned in the Puranas, Narasimha Avatara was the fourth incarnation of Lord Vishnu. The incarnation was in the form of a man-lion. The word Narasimha is derived from `Nara` means a man and `Sinha` a lion.
The idol of Narasimha widely worshiped in deity form by a significant number of Vaishnava groups. He is known mainly as the `Great Protector`, being a form of Vishnu or Krishna, who specifically defends and protects his devotees at the times of need.
In a mythical story as mentioned in Vishnu Purana it is said that one of the two doorkeepers of Vishnu`s paradise, came down to earth as a monarch, named Hiranyakasipu. Hiranyakasipu was pitiless, harsh and unjust. He behaved this way particularly towards his son named Prahlad. But he had obtained from Brahma, by severe penance, the boon that he should not be slain by any created being.
Hiranyakasipu became very proud, and required all persons to honour him by saying, `Om Hiranya` in adoration to Hiranya. If anybody did not say so he ordered that being to be punished. His son Prahlad, who was a devoted worshipper of Vishnu, would not obey his father`s order, but continued to say `Om Namah` meaning Om Vishnu.
Hiranya argued with his son Prahlad because of this, but it was vain. Then he attempted to punish and kill him, but in vain. Prahlad was struck heavily but did not feel the strokes. Then he was cast into the fire but was not burnt; he was trampled on by elephants, but continuing to think of Lord Vishnu he was not hurt. He was then again thrown confined into the sea but a fish carried him safely to shore. At last, when Prahlad did not cease praising Vishnu, and asserted that he was everywhere and in everything, Hiranya retorted. Prahlad rose and struck a column of the hall in which they were assembled; and behold, there issued from it Vishnu, in a form which was half-man and half-lion, and tore Hiranya to pieces.
Based on this story, it is believed by supporters that Narasimha protects his sincere devotees when they are in extreme danger.