Jambavan is also called Jamvanta, Jambavantha, Jambavat, or Jambuvan the King of the Bears, immortal to all but his father Vishnu. In the Valmiki Ramayana however, he was described as being a Vanara or monkey. He was known as Riksharaj. Rikshas are described as bears. He was created by Brahma, to assist Ram in his battle against Ravana. He was present at the churning of the ocean, and is supposed to have circled Vamana 7 times when he was acquiring the 3 worlds from Mahabali.
He was the King of the Himalayas who had incarnated as a bear in order to serve Ram. Jambuvan had received a boon from Lord Ram that he would have a long life, be handsome and would have the strength of ten million lions. Jambavantha was thought to be quite experienced and clever. Jambavan had a good knowledge of running a kingdom. Sugriva’s experts contained Jambavantha, Nala, Neela, Hanuman and a handful of others. Sugriva was living on mount Rishyamukha with these advisers. He advised Sugriva to send Hanuman to recognize Ram and Lakshmana, to find out who they were and what their intention was.
Later, it was he who made Hanuman realize his enormous abilities and motivated him to fly over the ocean in search for Sita.
Once during a duel with Ravan, Jambavan was fast and ferocious. He gave Ravana powerful blows with his hands and ultimately kicked him on his chest, knocking Ravan unconscious and making him fall flat in his chariot. Because of this, the charioteer withdrew Ravan from the battle. Previously, Ravana had dueled Hanuman, who is regarded as the incarnation of Lord Shiva.
Jambavan in Mahabharata
In the Mahabharata, he had killed a lion, who had obtained a gem called Syamantaka from Prasena after killing him. As stated by a Hindu legend, this gem was eventually renamed as the Koh-i-Noor diamond of the present day. Krishna was suspected of killing Prasena for the jewel, so he tracked Prasena’s steps until he discovered that he had been killed by a lion who had been killed by a bear. Krishna tracked Jambavantha to his cave and a fight started. After twenty-eight days, realizing who Krishna was, he submitted. Jambavan gave Krishna the gem and also presented him his daughter Jambavati, who became one of Krishna’s wives