Aja is the name of the king of the Surya Vamsha (solar dynasty). He was the son of Raghu (son of Dilipa), father of Dasaratha and grandfather of Rama. He was called Aja because he took birth in the brahma-muhurta, the auspicious moment before dawn.
As Aja is one of the names of Brahma, the king thought it appropriate to name his son Aja.
In the Raghuvamsa of Kalidasa (V.6) this event is recorded in memorable words. Aja went to the swayamvara (a ceremony where the bride chooses the groom with her own free will) of princess Indumati, daughter of the king of Vidarbha. On the way in a forest he saw a wild elephant and ordered his men to shoot the animal dead. When the elephant was pierced by an arrow, it changed into another form and informed Aja that he was a gandharva (celestial being) but due to a curse from a sage, he had become an elephant. As Aja helped him to get back his form, the gandharva gave some arrows to Aja which helped him with the hand of Indumati at the swayamvara. After Dasaratha’s birth, Indumati died suddenly due to the fall of Narada’s garland on her while asleep. Aja was inconsolable. ‘Ajavilapa’ (Aja’s lament) is an oft-quoted literary piece.