Photinus (Greek Φωτεινός; died 376), was a Christian heresiarch and bishop of Sirmium in Pannonia Secunda (today the town Sremska Mitrovica in Serbia), best known for denying the incarnation of Christ. His name became synonymous in later literature for someone asserting that Christ was not God. His teachings are mentioned by various ancient authors, like Ambrosiaster (Pseudo- Ambrose), saint Hilary of Poitiers, Socrates Scholasticus, Sozomen, saint Ambrose of Milan, Augustine of Hippo, John Cassian, Sulpicius Severus, Jerome (Eusebius Sophronius Hyeronymus), Vigilius of Thapsus (Vigillius Tapsensis) and many others.
None of his writings are extant and must be reconstructed through his critics.
Photinus grew up in Ancyra in Galatia, where he was a student and later a deacon of bishop Marcellus. Marcellus, in later life a staunch opponent of Arianism, was deposed in 336 but reinstated by the Synod of Serdica in 343, which also made Photinus bishop of Sirmium. In 344, the Synod of Antioch deposed Marcellus and drew up the Macrostich, a creed which listed their beliefs and objections to Marcellus' doctrines (among others). R. P. C. Hanson (1973) described Photinus' Christology as consistent with the early teachings of Marcellus. between 340-350.
At the time Photinus voiced his own theological system, according to which Jesus was not divine and the Logos did not exist before the conception of Jesus. For Photinus the Logos was simply a mode of manifestation of the Father, hence he denied the pre-existence of Christ and saw theophanies in the Old Testament as of the father, and the image of the "Son of God" (actually, Son of man) in front of (and distinct from) the Ancient of Days as prediction only. As a matter of fact, Photinus' apprehension of God as Father, and his teachings about the nature of Jesus Christ are maybe more complex than has been thought.