Answer by Raakhee Venugopal:
Uloopi was a beautiful Naga princess, the daughter of the Naga king Kauravya, who is said to have been overwhelmed by desire for the handsome Arjuna while he was bathing in a lake beneath which her palace was. She is said to have rendered him unconscious and dragged him to her realm under the lake.When he came to his senses, she expressed her love and requested him to marry her. Arjuna explains to her that he has undertaken the vow of brahmacharya for 12 years. She argues that it is a duty to relieve the distressed. She says that she would destroy herself if he were to shun her. And that he would only be acquiring merit by saving her life thus. After much persuasion, Arjuna finally obliges and marries her. He spends the night with her in her palace and then leaves on his further journey the next morning. As a parting gift, Uloopi gives him a boon that he will be invincible in water by saying, ‘Every amphibious creature shall, without doubt, be vanquishable by thee.’Years later, Uloopi is the one who incites Arjuna’s son Babhruvahana to fight and kill his father so that Arjuna may be freed of the curse inflicted upon him by the Vasus, the brothers of Bhishma, for having unfairly killed Bhishma in the Mahabharata war. She later revives him using the Naga gem.The Vishnu Purana and the Bhagavata Purana briefly mention a son born out of the relationship between Arjuna and Uloopi, named Iravan.