Who is Prahlada:
“Among all these living beings, cosmic godheads, superhuman and human and subhuman creatures, and amid all these qualities, powers and objects, the chief, the head, the greatest in quality of each class is a special power of the becoming of the Godhead. I am, says the Godhead, Vishnu among the Adityas, Shiva among the Rudras, Indra among the gods, Prahlada among the Titans,...".
Story of Prahalad and Holika:
According
to the Puranas, a king named Hiranyakashipu, like many asuras,
wished to be immortal. To fulfill this desire, he performed tapasya until
he was granted a boon by Brahma. The boon granted Hiranyakashipu:
that he would not die at the hands of any being created by Brahma, that he
would not perish inside or outside, by day or night, by any weapon, on the
earth or in the sky, by men or beasts, devas or asuras, that he be
unequalled, that he possess undiminishing power, and that he be the one ruler
of all creation.
His
wish granted, Hiranyakashipu felt invincible, and conquered the three worlds,
assuming the throne of Indra. He punished and killed anyone all those
who objected to his supremacy. His son Prahlada, refused to worship his
father as a deity. He was raised a Vaishnava and continued worshipping Vishnu.
This infuriated Hiranyakashipu, and he made various attempts to
kill Prahlada but failed. King Hiranyakashipu's sister, Holika, offered her
help. Holika told her brother that due to a boon she had received, she was
invulnerable to fire. Arrangements were made to have Prahlada sit upon the lap
of his aunt, atop a burning pyre. However, as Prahlada chanted the name of
Vishnu, he escaped unscathed, while Holika was incinerated.
(In
a variation of this Puranic legend, Holika wore her scarf or a fireproof
garment, so that Prahalad may perish, and she may be protected atop the pyre.
However, as the fire roared, the garment flew from Holika and covered Prahlada.
Thus, Holika was burnt to death, and Prahlada came out unharmed.)
Afterwards
, Vishnu appeared in the form of Narasimha (a half-human and half-lion avatara,
one not created by Brahma), at dusk (neither day nor night), took
Hiranyakashipu to his dwelling's threshold (neither indoors nor outdoors),
placed him upon his lap (neither land, water, nor air), and then slew the king
with his claws (not a weapon). In this manner, Prahlada and the races of the
three worlds were thus set free from the tyranny of Hiranyakashipu, and cosmic
order was restored.
(Source: Essays on the Gita, p.363, “God in Power of Becoming”)
(Source: https://en.wikipedia.org/wiki/Holika)