In the Puranas, Ganga is said to emanate from the toe of Vishnu and was brought to earth by the rishi Bhagiratha to purify the ashes of the 60,000 sons on King Sagara all of whom had been burned up by the rishi Kapila.
Interestingly, the descent of Ganga disturbed the sage Jahnu as he was performing yagya and he drank up all the water, but later relented and allowed the river to flow again.
Ganga is the eldest daughter of Himavat and Mena, and her sister was Uma, wife of Shiva. Later, Ganga was wife to King Santanu and bore a son Bhishma who was pretty much the central character in the Mahabharata.
