Hiranyakashipu and Hiranyaksha were both sons of Rishi Kashyapa and Diti. It’s believed they were conceived at a very inauspicious time during dusk, and both turned out to be fearsome, evil Asura.
Hiranyaksha was killed by Vishnu in the form of Varaha, when he abducted Bhoodevi, and took her into the ocean, plunging the three worlds into chaos. Furious at his brother’s death Hiranyakashipu swore revenge on Vishnu and did intense penance, finally Brahma appeared, and asked him for a boon.
That is when Hiranyakashipu asked
“Grant me that I not die within any residence or outside any residence, during the daytime or at nighttime, nor in the ground or in the sky. Grant me that my death not be brought about by any weapons or hands, nor by any human or animal. Grant me that I not meet death from any entity, living or nonliving created by you. Grant me, further, that I not be killed by any deity or demon or by any other organisms and divinities.”
Brahma granted him the boon, and Hiranyakashipu felt he was as good as invincble, as no one could satisfy those conditions. And conquering heaven, made the Devatas his slaves, and began to harass, persecute all Vishnu devotees, locking them up in dungeons, torturing them.
Hiranyakashipu’s son Prahlada was however a devout Vishnu bhakta much to his father’s chagrin.When Hiranyakashipu was unable to change his son’s mind, he ordered him to be killed. However at every attempt to kill him, Prahlada was saved. He even tried to get Prahlada burnt alive through this sister Holika, but it was she who ended up being burnt to death.
When Hiranyakashipu asked Prahlada where Vishnu was present, he replied he was omniscient, and found everywhere. He pointed to a pillar, and asked if his Vishnu was there, to which Prahlada replied “Yes he was and will be”.
When a furious Hiranyakashipu struck the pillar, the fierce form of Vishnu, Narasimha emerged, who was neither man nor beast. It was twilight, neither day nor night. He picked up Hiranyakashipu and took him to the threshold, neither indoors nor outdoors, and placed him on his lap, neither earth nor sky. And finally he killed him with his nails, tearing apart his stomach, which were not weapons.Vishnu had outwitted Hiranyakashipu as Narasimha, getting over and each every conditon in the boon granted by Brahma.