Sugreeva and Vali
Vali the son of Indra and Sugreeva the son of the Sun God were brothers. Their mother was a monkey called Aruni .Vali was the elder and became the king of monkeys and lived on Kishkinda Mountains. Vali was given a boon that he would absorb half the strength of the enemy facing him. Once an asura called Dundubi troubled them a lot. He was extremely powerful. So the brothers went to fight with Dundubi. The war went on for a long time. Being defeated Dundubi ran to hide himself in a cave. Vali decided to enter the cave to pursue the Asura. He asked Sugreeva to close the cave with a big stone and wait for hi outside. If blood comes out, he should assume that Vali is dead and crown himself as the king. Sugreeva waited for a long time. Dundubi by his magical powers made blood appear outside the cave. So Sugreeva assumed that Vali is no more and crowned himself as the king of monkeys. After some time Vali killed Dundubi and threw his body out of the cave. The body fell on a sage who was doing his prayers in Risha Mooka Mountains. The sage became very angry and cursed Vali that, if he enters the mountain he will die. Vali marched to Kishkinda and confronted Sugreeva. He was very furious. Though Sugreeva explained the facts, he refused to believe him. Sugreeva along with his supporters fled to the Rishya Mooka Mountains.
When he was living there, Rama with Lakshmana arrived near the mountains in search of his lost wife Sita. Hanuman who was the minister of Sugreeva met him and talked to him. He explained to Rama the situation of Sugreeva. Rama agreed to kill Vali and wanted Sugreeva to help him search for Sita.
Since Vali automatically would get half his power if he faced him, Rama sent Sugreeva to fight with him. Vali who looked very similar to Sugreeva thrashed him and sent him back. Because they were looking very similar, Rama could not help Sugreeva. So he put a garland on the neck of Sugreeva and sent him again to fight with Vali. This time when they were fighting, Rama sent an arrow from his hiding and killed Vali. Sugreeva was crowned as the king of monkeys. He helped Rama in finding out Sita and also helped him to recover her after killing Ravana.