One of the ethnic groups mentioned in Ṛgveda (Rigveda). The name Aja is mentioned in plural along with the names of two other ethnic groups—Śigru (Shigru) and Yakṣu (Yakshu)—
ajāsaśca śigravo yakṣavaśca/ valiṃ śīrṣāni jabhruraśvyāni

Aja, Śigru and Yakṣu clans were probably defeated by Tritsu and Paijavana Sudāsa (Shudasa). Based on the clues provided by hymns in Ṛgveda, Heinrich Zimmer has commented that the Aja-Śigru-Yakṣu people gathered under the supervision of the clan named Bheda to fight against Sudāsa.

See Vedic Index, vol. I, p. 12.