Ahilya + Surya = Vali + Indra = Sugriva AhilyA. She was the wife of Gautama, one of the seven great sages who appeared from the mind of lord BrahmA. Indra disguised himself as Gautama Muni and seduced AhilyA, who had been blessed that she would never age beyond sixteen. She was the most beautiful lady on earth, and both Indra and the sun-god became enamoured by her beauty. One after the other, Indra and the sun-god came to her in the form of Gautama Muni and had union with her, and Sugriva and VAli were born as a result, respectively (Sugriva of Indra’s union and VAli of Surya’s union). http://www.salagram.net/sugriva.htm