Kumbhakarna appeared in the Ramayana in a line of rebirths that started in Brahma’s court in heaven (svarga). In that lifetime he had been Vijaya, one of a pair of twin doorkeepers who were cursed for not properly performing their duties. He was reborn as Hiranyakasiipu and killed by Vishnu in his Narasimha incarnation (avatara). Next he was reborn as Kumbhakarna, to be killed by Vishnu in his Rama avatara.
Kumbhakarna was a son of Visravas by his rakshasa (night-wandering demon) wife Keshini. He was a full brother of Ravana. The brothers practiced such power austerities (tapas) that the gods became frightened. They had Saras- vati (goddess of learning) dance on Kumbhakarna’s tongue when he asked Brahma for a boon. Kumbhakarna was going to ask for annihilation of the devas (nirdevatvam), but with Sarasvati dancing on his tongue, he asked for sleep (nidravatvam). So that was what Brahma gave him. Kumbhakarna slept for six months and then was only awake for a day. When the war was going poorly for Ravana, Kumbhakarna was awakened, readied for battle with two thousand pots of liquor, and sent against Sugriva, the great monkey warrior. Kumbhakarna was able to defeat Sugriva by pounding him into submission with a giant boulder, and then carried him into Lanka as a prisoner. He returned to the battle and met Rama in single combat. But after a great fight, Rama cut off his head.
Kumbhakarna’s advice to Ravana during various phases of the war showed that he judged his brother’s actions as wrong and yet did his duty as a younger brother. In Brahmanical orthoprax morality Kumbhakarna had done his duty in that birth. He was reborn as Dantavaktra, a Danava king of Karusha, to be killed by Vishnu in his Krishna avatara. Then he returned to Vaikuntha, the abode of Vishnu.