Aruṇa (Aruna) is one of the varga(s) or gaṇa(s) (gana; genus or sect)of the ṛṣi(s)(rishi; sage) , as mentioned in Taittirīya Āraṇyaka (Taittiriya Aranyaka). Here it is said that Prajāpati (Prajapati; Lord of the people) Brahmā (Brahma)sat in meditation, for conceptualising the Creation. Contemplating on how the Creation would be, he shook the mass of his body, and from that stirring mass, three kinds of sages were born, classified under three varga(s). Aruṇa was one of these gaṇa(s) —

sa tapastaptvā śarīramadhūnata.
tasya yanmāṃsamāsīt, tato aruṇā
ketavo vātaraśanā udatiṣṭhan.