Bhūta was a sage. Prajāpati Dakṣa (Prajapati Daksha) married off his two daughters to him. One of the daughters was named Sarupā (Sarupa; according to another variation her name was Surabhi). Eleven Rudra were fathered by him to Sarupā. Aja was one of them. Every Rudra was the lord of many other Rudra, i.e., the chief of a gaṇa (gana; group). Therefore, Aja was also the chief of a gaṇa.