A son of Ravana.
After Brahma created the universe, he felt quite proud and decided to rest for a while. To teach him a lesson, Vishnu released earwax which became two rakshasas called Madhukaidabhas. On hearing their raucous laughter, Brahma was frightened and approached Vishnu for help. Since his ploy was succesful, Vishnu called the Madhukaidabhas and told them he would give them a boon. They countered that they would give Vishnu a boon. So Vishnu said that he would like the permission to kill them, as a boon. They said that they would not go back on their word, but since their lust for battle had not been quenched, Vishnu should take care of that. Vishnu agreed, but said that the boon he got needed to be done with first. Vishnu told them that later, they would be born as Khara and Atikaya in the Tretayuga, and that he would himself kill Khara in the form of Rama, and Atikaya would be killed by Lakshmana, an incarnation of Anantha. Thus each would fight a battle that would quench his thirst. So saying, he placed each rakshasa on a thigh, and killed them with them with the sudarshan chakra, according to Kambaramayana Yudhakanda.
The Kambaramayana Yudhakanda further describes his birth and other details. When Ravana was returning in the Pushpakavimana after defeating Kuber, he saw a few gandharva women in the foothills of Mayuragiri. Their leader was Chitrangi, wife of Chitrangada. Ravana managed to seduce her and have a child with her. She left the child with Ravana and returned to the heavens. Ravana placed the child in the Pushpakavimana and resumed his journey. But the vehicle struck Girishringa and the child was thrown into the jungle. When Ravana searched for the child, he found that it had landed on a rock, but remained unhurt. Ravana tried to lift the baby but couldn’t do so in spite of using ten of his hands. Meanwhile the baby started growing. Ravana used twenty hands and the baby grew further. Finally it got into the pushpakavimana by itself. Ravana named him Atikaya and placed him under the care of Dhanyamala, in Lanka.
Atikaya began praying to Brahma in Gokarna. Brahma appeared, but Atikaya was so lost in meditation that he didn’t realise Brahma’s presence. He had even stopped breathing. Brahma used his power to force air into Atikaya, and rejuvenate him. Following that he gave Atikaya three blessings – the brahmastra which could annihilate anyone, a jacket which nothing could pierce, and the absence of thirst and desire.
Atikaya trained under Shiva in Kailash. After completing his education, Atikaya asked Shiva what he’d like as gurudakshina. Shiva asked Atikaya to promise that he would never use maya as a weapon. Atikaya did so, and Shiva was pleased enough to give him the Pashupatastra.
Atikaya had an uncle named Chandra, who once lost to Indra. He was brooding over that when Atikaya arrived in Lanka with the pashupatastra. He asked Atikaya to capture Indra. Atikaya fought with Indra but Vishnu arrived there and helped Indra with the sudarshan chakra. Atikaya countered that with the pashupatastra. Vishnu learned who Atikaya was and withdrew himself from the fight. Indra agreed that he had been defeated.
During Rama’s war with Ravana, Lakshmana killed Atikaya after a long fight.