Vali-Sugreeva. Epic Characters of Ramayana

Vali and Sugreeva were born to a vanara maiden as a boon from Indra and Suryadeva respectively. Vali was crowned the king of Kishkinda. As a result of a number of boons he became invincible. When Ravana challenged his might, he simply carried the demon under his arm and smashed him down thus humiliating him. Ravana had to bow down to him and seek his friendship. There ensued a battle between Vali and  Dundhubi, who came in the form of a wild buffalo.
Vali destroyed him completely and hurled him in the sky. In doing so, the blood from the dying animal defiled Sage Matanga's ashram due to which the sage cursed Vali and the vanaras saying that whoever came near his ashram would fall down dead. Mayavi, Dundubhi's brother, retreated into a cave after challenging Vali. Vali followed him in leaving Sugreeva guarding the mouth of the cave. Poor Sugreeva who had been sworn not to enter the cave stood guard for more than a year after which he heard the loud scream of the rakshasa and then saw blood streaming out.
Thinking that Vali had been killed, he shut the mouth of the cave with a boulder  with the intention of preventing further damage at the hands of the demon. However, Vali returned, accused Sugreeva of usurping his place by deceit and banished him from Kishkinda. Sugreeva later on forged friendship with Rama and Lakshmana, killed Vali and helped Rama get back Sita after commanding an army himself at the  battle of Lanka.
On his deathbed, Vali heard Rama speak about dharma and made peace with Sugreeva. He asked him to take over the responsibility of the kingdom, his son Angada and his wife Tara. Sugreeva repented for bringing about his brother's end, performed his last rites and helped him reach heaven. When Rama decided that it was time for him to get back to vaikunta, the purpose of his incarnation being over, Sugreeva was among those who accompanied him.