The birth of Bali and Sugriva.
Maharishi Kashyapa’s wife Vinita once laid two eggs but they did not hatch for a long time. Impatient, Vinita broke one of the eggs. The child that emerged from the broken egg, was incomplete in that its lower extremities were not formed. It had no legs or genitals. Out of motherly affection, Vinita named her malformed son Aruna, God of Dawn (In the Vedas, we identify this god as Ushas) and over a period of time, Aruna became the charioteer of Lord Surya.
Since Aruna was without any genitals, no body was sure whether the child was a male or a female.
One day, sage Mandavya saw a woman carrying in a basket her sick husband to the house of a prostitute, because that is what he desired.
Unfortunately while carrying her head load Nalayani hit sage Mandavya and he became furious and cursed that her husband would die by the next sunrise. Horrified at these developments, Nalayani used her powers of chastity and prevented the sun from rising. Lord Surya’s chariot stopped in midway, giving Aruna an opportunity to take a break – a rare event in Aruna’s life.
During this forced respite Aruna changed his form into a woman and entered the celestial city of Amaravathi, under the name of Aruni, to watch the dances of the Apsaras, which was forbidden for all males except Lord Indra. When Lord Indra espied Aruni he was aroused, and their union resulted in the birth of Vali.
On learning of the transformation of Aruna into Aruni, Lord Surya wanted to see Aruna in the female form of Aruni, and in due course he also had intercourse with Aruni.
Out of this union Sugriva was born. Both the children were adopted by Ahalya wife of the sage Gautama. Once, the two boys disobeyed Sage Gautama and out of rage he cursed them to be turned into monkeys and the monkey King Riksha ruler of Kishkinda, adopted them as his children, as he was also childless.
Moral of the story : In our Puranas, there is always a constant rivalry between Lord Indra and Lord Surya. And this rivalry extends to their sons. Ramayana gloats over Vali-Sugriva Vadham. In the Mahabharata it is the rivalry between Arjuna and Karna.
One of the meanings of Vanara may also be “the people of the forest”. Vana = Forest and Nara = people.