Narasimha is the fourth avatar of the Lord Vishnu. He is believed to have taken the avatar to destroy the demon King Hiranyakashipu. Narasimha is visualised in a human-like body with a lion-like face and claws. In Bhagawat Purana, it is described that as Varaha, Lord Vishnu killed Hiraṇayakṣa.
In continuation, the legend goes as below:
Hiranayaksa’s younger brother, Hiranyakashipu wanted revenge from Lord Vishnu for the death of his brother. After many years of his austere penance, Lord Brahma offered him the boon of immortality on conditions that he cannot be killed by man or beast or devil or god. He cannot die in day or night. Steel or stone or wood, indoors or outdoors, or on earth or sky, Hiranyakashipu can die nowhere and by no one. After securing his death wishes, Hiranyakashipu became a tyrant with his intent to conquer everything.
Hiranyakashipu and his wife Kayadhu gave birth to Prahlad, who grew up to became an ardent devotee of Lord Vishnu. Hiraṇyakaśhipu was furious at the devotion of his son to Lord Vishnu. The king challenged his son to prove his devotion to Lord Vishnu. He heated an iron pillar and then asked Prahlad to embrace it to confirm Lord Vishnu’s presence. Prahlad rushed towards the pillar and squeezed it. The heated iron pillar did not burn him. The king in his fury hit the pillar with his sword. The pillar was transformed into Narasimha, an avatar of Lord Vishnu with a thundering sound.
Narasimha was half lion and half man. This happened during twilight hours, which was neither day nor night. He sat on the threshold of the court room which is neither inside nor outside and pierced his nails into the body of Hiranyakashipu and opened his stomach. The demon king was killed in a moment. Prahlad’s belief in Lord Vishnu was rewarded and once again, the world was saved from a tyrant.
Source: https://www.brihaspatipuja.org/narasimha-avatar.html