Rao Sonag was a Rajput king belonging to the Rathore clan, and the first Rao of Idar. His father was Rao Sheoji and his mother hailed from the Chavda clan of Rajputs.
Sonag was a brother of Rao Asthan, ruler of Khed. The two brothers together conquered the town of Idar and Sonag settled there. Consequently, his descendants are known as "Idariya Rathores."