Hiranya kashyap is believed to be the first demon child of Maharishi Kashyap and Diti. Three demons had taken over the throne of Indra Hiranya kashyap, Prahlad and Bali. After that the throne of Indra went back to the devtas (deities) forever.
Hiranya kashyap was born to Diti at the time when she was sitting on the throne of Hiranya (gold) for the Ashvamedh Yagya performed by Maharishi Kashyap. That is why he was called Hiranya kashyap. His brother Hiranyaksha was killed by Lord Vishnu.
Hiranya kashyap got very angry with this devotion of Prahlad towards his enemy Vishnu and many times he tried to kill Prahlad, but every time Prahlad was saved.
According to many ancient stories, it is said that Hiranya kashyap’s wife Kayadhu not only was a great devotee of Vishnu but at the same time was a devotee of Devi Ganga and was loved by Devi Ganga. Gangamaiya had protected Kayadhu’s son Prahlad from the fatal conspiracies of Demon priest Shukracharya.
Fed up with the atrocities of Hiranya kashyap, the devtas (deities) pleaded Lord Vishnu to kill him. In the end, Lord Vishnu manifested from a stone pillar in His Narsimha (half lion, half human) avatar (incarnation) , and at twilight killed Hiranya kashyap with his nails, thus cleverly circumventing the boon given him by Brahmaji.