Who is Lord Nrisimhadeva!

By performing the rigorous austerity  Hiranyakasipu received benedictions from Lord Brahma that he could not be killed in the day or in the night, he should not die on land or in the air or in the water, he would not be killed by any human demigod or animal, he could not be killed by any weapon etc: Lord Brahma agreed.

After receiving these benedictions Hiranyakasipu became more demonic and began conquering the material universe.

In time Hiranyakasipu had a son called Prahlada. Prahlada was a great devotee of Lord Krishna even from birth. As a small boy of five he would preach about Krishna to his school friends any time the teachers left the room. Prahlada's preaching infuriated his father, Hiranyakasipu.

Hiranyakasipu became so angry that he ordered Prahlada to be killed. Despite all his efforts to kill his five year old son, Pralad was always protected by the Lord. Neither boiling in oil, nor poison, not being thrown off a cliff, nor being thrown in fire, nor being trampled by elephants could harm pralad.

But Prahlada kept chanting Hare Krishna and he was protected by Krishna's holy name.

Hiranyakasipu, seeing that none of these things could kill Prahlada.

Since through all this Prahlada was not harmed, Hiranyakasipu thought he must have some mystic power.
Hiranyakasipu demanded to know where he got his super human powers from.

Prahlada replied that he got his strength from the same place as Hiranyakasipu did--from God. Hiranyakasipu demanded to know what was this God where was this God. Prahlada explained that God is everywhere that everything comes from God. Hiranyakasipu, despite all that had happened, could not believe in God and began pointing to things demanding if they were God. Hiranyakasipu demanded if God was in a big pillar nearby in the palace. When Prahlada said, "Yes, my Lord is in that pillar," Hiranyakasipu stated that he would kill Prahlada's God by using his mace to smash the pillar. As he smashed the pillar Lord Nrsimhadeva, the half man, half lion incarnation of Krishna appeared from the broken pillar and pounced on the shocked demon.

Nrsimhadeva stretched Hiranyakasipu across his lap and with his long nails, he ripped apart the demon. Hiranyakasipu died instantly on Nrsimhadeva's blood drenched lap. He was killed neither on the land, sea nor in the air but on the lap of the Supreme Lord. He was killed neither during the day or the night but in the twilight. He was killed by neither beast nor man, but by the lord's lotus hands and was kill with no weapons but with the nails of Lord Nrsimhadeva. Thus Hiranyakasipu's benediction from Lord Brahma remained intact and he was killed by the personification of fear, Krishna Himself in His half-man, half-lion form, Lord Nrsimhadeva.