Story of Lord Narasimha

Hiranyakashipu (the brother of Hiranyaksha who was killed by the Varaha Avtar) wanted to take revenge on the Devatas and in particular on Lord Vishnu. He wanted to become the master of all the three worlds - Heaven, Earth & Pathala. He went to Mount Mandarachala and began penance which continued for years. Due to the intensity of Penance, Lord Brahma appeared before Hiranyakashipu and Hiranyakashipu asked for immortality as boon. Brahma, however, declined, saying "All living beings must face death Hiranyakashipu. You can, however, choose your death wish."
Hiranyakashipu then asked for three conditions, as his death wish, "'O Brahma, let not death come to me either by man or beast, nor devil, nor god shall cause my death by day or by night with steel or stone or wood, indoors or outdoors, or earth or in sky. Grant me undisputed lordship over the world". Brahma agreed and Hiranyakashipu got his death wishes granted. Thus he became practically immortal. After securing such a boon Hiranyakashipu conquered the worlds and became a tyrant. He banned all poojas on Vishnu and declared himself as God. The Devtas approached Lord Vishnu for help. Lord Vishnu asked them to be patient and said, "Hiranyakashipu' s son Prahlad is a devotee of me. When Hiranyakashipu seeks to kill my devotee I will slay him." Hiranyakashipu's wife Kayadhu gave birth to Prahlad in the Ashrama of Narada who told Prahlad about the glory of Lord Vishnu. Prahlad grew up and became an ardent devotee of Vishnu. Hiranyakashipu, however, wanted his son to be the king of the Asuras, strong and ruthless. Realising that Prahlad always prayed to Lord Vishnu, Hiranyakashipu took his son to Shanku and Amarka, the sons of Shukracharya, for schooling. All their efforts to inflence Prahlad failed.
Hiranyakashipu ordered his servents to kill Prahlad if he refused to accept the supremacy of his father. They tried to kill him by throwing down a mountain, drowning, poisoning, burning etc. and failed in all attempts since Lord Vishnu saved him from all the attempts. The king got angry on hearing the reports about Prahlad. One day the king challenged his son in the open court:
"Prahlad! Is my enemy, whom you worship, present anywhere here?".
Prahlad replied, "Vishnu is omnipresent. There's not a single place where he's not found."
Hiranyakashipu's fury was at its climax. He got an iron pillar heated and asked Prahlad, "Can you embrace this pillar if your Vishnu is in it also?"Prahlad did not hesitate even for a moment but rushed towards the pillar and embraced it. The heated iron did not burn him. The king got up from his throne in fury and hit the pillar with his mace.
And to his surprise! The pillar cracked with a thundering sound and Vishnu appeared there in the form of Narasimha.
One half of his body was of a lion and the other half of a man. He had matted hair on his head, large moustaches on the face and terrible teeth in the mouth. His paws had terrible nails on them.
Hiranyakashipu remembered his first death wish, "To be killed by some one who is neither human nor beast." It was also the twilight hour, neither day nor night, the second death wish.
The demon king hit Narasimha with his mace but Narasimha brushed it aside swiftly. It was twilight and Narasimha caught hold of the demon Hiranyakashipu.
He sat on the threshold of the court room, placed the body of the demon on his thighs, and pierced his nails into the body of the demon and broke open his stomach. The demon was killed on the spot in a moment. The place was neither inside nor outside. This was Hiranyakashipu’s third death wish.
Lord Narasimha was furious and roared. However, he was passified when Prahlad touched his feet and goddess Lakshmi also tried to cool him. Lord Narasimha then made Prahlad the King.