Asterius the Sophist was a 4th-century Christian theologian, active during the reign of Emperor Constantine and the intense religious debates that followed. Originally a professional teacher of rhetoric, he converted to Christianity and became a prominent defender of Arianism. This theological position, which was condemned by the Council of Nicaea in 325, argued that the Son of God was not fully co-eternal or equal to God the Father. Asterius was a disciple of Lucian of Antioch and used his sophisticated rhetorical training to become one of the most articulate literary voices for the Arian party after the council.

His major work was a systematic defense of Arian doctrine, often called the Syntagmation. The full text is lost, but substantial fragments survive because they were quoted and refuted by his powerful opponents, such as Athanasius of Alexandria. Asterius is also credited with a Commentary on the Psalms, though only fragments remain. According to historical accounts from his critics, he may have renounced his faith during a period of persecution early in the century, a fact later used to attack his credibility. The exact date of his death is not known, but he was still active around 341 CE.

Modern scholars see Asterius as a significant figure because he represents the intellectual depth of early Arian theology. His arguments required serious engagement from defenders of the Nicene Creed, and the very fact that his work was preserved through their refutations shows he was considered a major threat. His surviving fragments offer important insight into the biblical and philosophical reasoning of non-Nicene Christianity in the 4th century.