Rishyashringa was the son of Vibhandaka, a forest rishi. By practicing austerities, Vibhandaka sought to acquire powers that could cause rain to fall or cause infertile couples to bear children.
The god Indra, fearful of Vibhandaka's powers, sent a heavenly apsara to tempt him.
When Vibhandaka saw the apsara, his semen spurted forth and fell to the ground. A doe ate the semen and gave birth to a child, a beautiful boy with the antlers of a deer. That boy was Rishyashringa.
Vibhandaka then raised Rishyashringa in complete isolation, seeking to protect him forever from the females of any species.
Inspired by: Sita: An Illustrated Retelling of the Ramayana by Devdutt Pattanaik
Notes: This story is on p. 13 of the book.