The daityas are a clan of asuras. They are the descendants of Rishi Kashyapa and his wife Diti. Kashyapa was the son of Marichi, who was one of Brahma’s six sons. Thus, daityas are the elder half-brothers of the devas, who are the descendants of Kashyapa and Aditi. Daityas and devas used to reside together in Swarga Loka during the Satya Yuga, but were jealous and fought with each other. The devas defeated the daityas and banished them from Swarga Loka. The daityas then took refuge in the Vindhya mountains in Central India. The Narmada became the sacred river of the daityas and many of them performed penances on its banks to obtain boons.
The Vishnu Purana says after being expelled from Swarga Loka, the daityas, along with their half-brothers Danavas and Nagas, established seven realms—Atala, Vitala, Nitala, Mahatala, Sutala, Patala and Gabhastimata. Once Rishi Narad went on a tour of these realms. He realised that the seven nether worlds were more beautiful than Swarga.
The daityas frequently attacked the devas and disrupted religious ceremonies, but a few daityas had a pious nature. Some even attained great fame. Hiranyaksha obtained a boon from Brahma, of not being killed by any god, man or beast. He terrorised the three worlds by submerging the earth in the cosmic ocean. It was rescued by Vishnu after killing Hiranyaksha in his Varaha (man-boar) avatar.
To avenge his death, his elder brother Hiranyakashipu obtained a boon from Brahma that he could not be killed by human or animal, either inside or outside the house, by day or by night, and that no weapon could harm him. Armed with this boon, he started harassing the three worlds, going to the extent of trying to kill his son Prahlada for being a devotee of Vishnu. Vishnu finally killed him in his Narasimha (man-lion) avatar.
The grandson of Prahlada, Mahabali, was a benevolent and generous daitya king. People were very happy under his rule. He had conquered heaven and earth. The devas approached Vishnu, but he refused to intervene in their war or to kill his devotee, Mahabali. To help them, however, he incarnated as Vamana (dwarf Brahmin). Vamana requested Mahabali for ‘three steps of land’. Mahabali granted the boon, though he was warned by a suspicious Shukra. Vamana expanded his form and covered the heaven and earth in two steps. Bali offered his own head on which Vamana took his third step pushing him down into Patala Loka. The festival of Onam is celebrated with much fanfare in Kerala where it is believed that on this day, Mahabali comes up from Patala to visit his former subjects.