The Story of Sugriva is mentioned in the great epics of Ramayana .
In Ramayana it is mentioned that, Bali was the emperor of Kishkindha, the country of the monkeys or the Vanaras. Bali's wife was Tara and Sugriva was his brother. According to the legend one day a raging demon came to the gates of Kishkindha and challenged Bali to a fight. Bali accepted the challenge but when he ventured towards the demon it fled in terror into a deep cave. Bali entered the cave in pursuit of the demon, telling Sugriva to wait outside. Sugriva waited for Bali and heard demonic shouts in the cave and seeing blood oozing from its mouth, he concluded that his brother had been killed. With a heavy heart, Sugriva rolled a boulder to close up the cave's opening so that the demon cannot get out. Then Sugriva returned to Kishkindha and was made the emperor of the Vanaras and married Tara.
However Bali succeeded in his fighting with the demon and returned home. There he saw Sugriva as the king. Bali concluded that his brother had deceived him. Although Sugriva wanted to explain, Bali did not listen. In his rage Bali threw his younger brother out of the kingdom. As a result the two brothers became bitter enemies.
When Sugriva was in exile he made friendship with Lord Rama, the avatar of Vishnu. Rama was then in expedition to rescue his wife Sita from the clutches of demon Ravana, Rakshasa King of Lanka. Rama promised Sugriva that he would kill Bali and would make Sugriva the king of the monkeys. Sugriva consecutively promised to help Rama in his expedition.
Sugriva and Rama together, went in search of Bali. While Rama stood back, Sugriva challenged Bali to a fight. Since the brothers looked identical and indistinguishable Hanuman (Sugriva's counselor) stepped forward and placed a garland of flowers around Sugriva's neck. It was then that Lord Rama emerged could kill Bali.
Then Sugriva helped Rama by sending his trusted advisor Hanuman to determine where Sita was kept as a prisoner by Ravana. It was Sugriva's army that helped Lord Rama to build the bridge on the river. This bridge helped the entire army to reach Lanka.
Sugriva during the battle attacked Kambhakarna, the brother of Ravana who almost killed by him. Seeing the demon in the middle of the fight, Sugriva attacked him with the trunk of a Sala tree. The tree, however, merely broke over the demon's head. Kambhakarna then seized Sugriva and dragged him off, and then Rama's brother Lakshmana rescued him.