Greek theologian and bishop of Ancyra (now Ankara, Tur.) whose attempt to mediate a controversy in the Eastern Church was rejected by the heretical faction and brought about his exile.

Basil, a physician, was nominated bishop in 336 by the Semi-Arian party (see semi-Arianism). In a Synodal Letter sent to all bishops summarizing the conclusions of a local council in Ancyra (358), Basil's clear enunciation of the Semi-Arian viewpoint established him as that group's intellectual leader.

Despite the efforts of Basil and his colleagues, the Arians (see Arianism) gained the support of the emperor Constantius II (ruled 337–361) and repudiated Basil's formula at two councils convened in 359. Basil's party was compelled by Constantius II in December 359 to sign the heretical Arian formula of Ariminum. The Arians, led by Bishop Acacius of Caesarea, met in synod at Constantinople in 360, deposed Basil, and banished him to Illyria.

Before his death, however, Basil recanted his signature of the Arian formula extorted from him by the Emperor. The orthodox party, represented by Athanasius of Alexandria and Hilary of Poitiers, acknowledged that Basil's formula approximated their own and urged others to seek a consensus with him.

Among Basil's other writings is a treatise on virginity, which suggests that this virtue can be secured on the basis of bodily harmony fostered by an ascetical life.