Phoebadius of Agen was a fourth-century bishop from Gaul who lived and died in Agen. A staunch defender of Nicaean orthodoxy, he actively opposed Arianism during several ecclesiastical gatherings, including the Council of Ariminum in 359. He worked alongside figures like Hilary of Poitiers to combat Arian influence throughout the region. Although many of his writings are lost, his surviving treatise against the Arians is noted for its logical strength and masterful composition.