Lucifer, bishop of Cagliari, was sent by Liberius the bishop, with Pancratius and Hilary, clergy of the Roman church, to the emperor Constantius, as legates for the faith. When he would not condemn the Nicene faith as represented by Athanasius, sent again to Palestine, with wonderful constancy and willingness to meet martyrdom, he wrote a book against the emperor Constantius and sent it to be read by him, and not long after he returned to Cagliari in the reign of the emperor Julian and died in the reign of Valentinian.
Source: De Viris Illustribus (Illustrious Men) (New Advent)