Hidimbi, in the Hindu epic Mahabharata, is a Rakshasi. She met Bhima while he was travelling in the forest with his Pandava brothers and mother Kunti. After fleeing a burning palace at Varanavat, which was set up by their cousin Duryodhana to burn them alive; the Pandavas were wandering in the deep woods at night. Hidimbi's brother, Hidimba, an alleged cannibal, had sent her to bring him manflesh, but when she saw the handsome prince Bhima sitting in the glade she fell in love with him and could not bring herself to kill him. She transformed into a tall, dark-skinned and immensely beautiful woman dressed in ornaments and garlands and approached him. When Hidimbi was late, Hidimba came to kill Bhima himself. He tried to attack Hidimbi but she was protected by Bhima, who killed Hidimba after a good fight. Hidimbi then asked Bhima to marry her, at which he was reluctant initially but finally ensued after being repeatedly insisted. He agreed to spend the time from dawn to dusk with her on the condition that during the dark hours he would remain with his brothers, and this would continue till they had a son. She eventually bore Bhima a son, Ghatotkacha. When the Pandavas left the forest, Bhima had to leave her as they were on a war campaign. It isn't clear whether they ever met again.
It is suggested by the similarity of their names that Hidimba and Hidimbi were twins.
It may be noted here that in certain parts of Himachal Pradesh Hidimbi (or Hidimbaa) is worshipped as a goddess. There's a temple dedicated to her in Manali.