Short answers, pulled from the story.
Prahlada is an asura prince in Hindu scriptures, known for his unwavering devotion to the god Vishnu despite being born to Hiranyakashipu, a demon king who despised Vishnu. He is celebrated as a model of bhakti and is a central figure in the Bhagavata Purana, the Vishnu Purana, and the Bhagavad Gita.
Hiranyakashipu was the ruler of the asuras and Prahlada's father. He held a vendetta against Vishnu and was infuriated that his own son refused to worship him and instead devoted himself to Vishnu. He attempted to kill Prahlada multiple times, including through poison, armed soldiers, elephants, snakes, fire, and submersion under mountains.
Narasimha, the half-man half-lion avatar of Vishnu, emerged from a stone pillar inside the palace and placed Hiranyakashipu across his thighs at the threshold of his home at dusk. He killed the demon king with his sharp nails, satisfying every condition of Brahma's boon by using a form neither fully man nor animal, at a location neither indoors nor outdoors, at a time neither day nor night, with no man-made weapon.
Holi commemorates the failed attempt by Holika, Hiranyakashipu's sister, to kill Prahlada by sitting with him on a burning pyre. Holika carried a boon of invulnerability to fire, but when Prahlada prayed to Vishnu, she was burned to ashes while he remained untouched. The festival marks his survival and the destruction of evil.
In chapter 10 verse 30 of the Bhagavad Gita, Krishna states: "Among the Daityas, I am the great devotee Prahlada and of calculators, I am Time; among quadrupeds, I am the lion; and among birds, I am Garuda." This declaration places Prahlada alongside cosmic forces as one of Krishna's supreme manifestations.
Major pilgrimage sites include Ahobilam in Andhra Pradesh's Nandyal district, the Yadagirigutta Temple in Telangana, Prahlad Ghat at Hardoi in Uttar Pradesh, and the Narsimha Temple at Sikligarh Dharhara in Bihar's Purnia district, which holds a 1,411-long pillar called the Manikya Stambha. The Prahladpuri Temple in Multan, Pakistan is also associated with Prahlada.