Saint Ruru is a hermit famous in the Hindu Puranas.
According to Devi Bhagavata (Skandha 2), Puloma was the wife of Bhrgu. He got the son Chyavana by Puloma. Chyavana married Sukanya. Pramati was born to them. The hermit Pramati married the beautiful damsel Pratapi and got a son named Ruru. He grew up to become a famous hermit.
Ruru happened to encounter exceedingly beautiful Pramadvara, the daughter of Visravas and Menaka and momentously fell in love with her. The father of Pramadvara came to know of this and decided to give her in marriage to him. During the marriage preparations, Pramadvara was bitten by a snake and fell down dead.
Ruru was greatly sad and disappointed. By his determination and sacrifising half of his life to her, Pramadvara came to life again and Ruru married her.
According to Mahabharata (Adi Parva), Ruru developed relentless hatred against serpents. He wandered about destroying every serpent he came across. Finally he confronted Dundubha, he was given exhortations and good advices regarding righteousness. Saint Ruru had taken a lively interest in the snake sacrifice known as Sarpa Satra held by king Janamejaya which was meant to exterminate all serpents.