Lucifer Calaritanus (d. May 20, 370 or 371) was a bishop of Cagliari in Sardinia known for his passionate opposition to Arianism. At the Council of Milan (c. 354 or 355), he defended St. Athanasius against Arian attempts to secure his condemnation by Western bishops. It was reported that Constantius II, a supporter of Arian theology, confined Lucifer for three days in the Imperial Palace, where Lucifer continued to argue venomously on behalf of Athanasius.