Vishnu's incarnations are known avatars and the Hindu scriptures mention 'Dhasavatharam' which refers to a collective of ten avatars known as Matsya, Kurma, Varaha, Narashimma, Vamana, Parasurama, Rama, Krishna, Balarama, and Kalki.
The Narashimma avatar is known as the fourth incarnation where Lord Vishnu descended to earth in the form of a half-man and half-lion to protect his devotee from a powerful demon. Check out the legend associated with the 'Narashimma' avatar:
Hiranyakashipu Receives The Boon Of Immortality
Hiranyakashipu is a powerful demon king who wanted to become the undisputed god of the universe. He mercilessly killed anyone who refused to worship him and the devotees of Lord Vishnu. To fulfill his desire of becoming immortal, Hiranyakashipu goes through an intense penance. His prayers to Lord Brahma were so intense and powerful that the Devas who reside in heaven could feel the heat.
Lord Indra, the king of heaven, who realized the demon king's absence seized the opportunity to attack Hiranyakashipu's kingdom with full force and took hostage of Hiranyakashipu's pregnant wife Kayadhu. His plan to take Kayadhu as a prisoner, however, was interrupted by Naradha Muni who took her to his ashram as she had nowhere to go. During her stay there, Kayadhu listens to stories of Lord Vishnu and developed a sense of attachment for him. Later, she delivers her son Prahlada at the ashram, who turned into Lord Vishnu's loyal devotee.
Meanwhile, Lord Brahma who was pleased with Hiranyakashipu's devotion appeared before him and offered him any boon, anything except for immortality. Hiranyakashipu requests a boon, a boon that would allow no man, god, or animal created by Brahma to kill him; no one could kill him in heaven or earth, during the day or night, indoors or outdoors, or with any weapon. Brahma happily grants his wish!
Lord Vishnu Protects His Loyal Devotee
Hiranyakashipu got enraged upon returning to his destroyed kingdom. To seek revenge, he single-handedly defeated Lord Indra and conquered his kingdom. Later, he brought his wife and son to his kingdom.
The demon king, however, was unhappy after learning about his son's devotion to Lord Vishnu. He laid traps to kill Prahlada many times and after many failed attempts, Hiranyakashipu mocks Prahlada and asks if Lord Vishnu can appear anywhere, even in a pillar. When Prahlada answered yes, the demon king kicked the pillar, and Lord Vishnu appeared in the form of Narashimma to protect his devotee.
The man-lion avatar dragged Hiranyakashipu to the threshold of the door - which was neither indoor nor outdoor, placed him on his lap - which was neither sky nor earth, and killed him using his claw which was not a weapon. Upon Hiranyalashipu's demise, Prahlad became the king of his father's kingdom.
Source: The Hindu Portal, Times Now News, Temple Purohit, Hindu Pad & Learn Religions.
Image credit: Religion World