Lucifer of Cagliari was a 4th-century bishop in Sardinia known for his intense opposition to Arianism. Serving as an envoy for Pope Liberius, he defended Athanasius of Alexandria during the Council of Milan in 355. Because of his refusal to yield to imperial religious policies, he faced imprisonment and multiple exiles, including periods in Palestine and Egypt. A scholar of Greek and Hebrew, he remained a strict adherent to Nicene theology, even refusing to reconcile with bishops who had previously compromised with Arianism, a stance that led to his followers being called Luciferians.