Diodore of Tarsus was a Christian theologian and bishop in the 4th century CE. Born in Antioch, he was educated in Greek philosophy before leading a monastery there. He was a prominent defender of the Nicene Creed against alternative theologies like Arianism. After 378 CE, he served as the Bishop of Tarsus until his death, which is estimated to be around 390 CE. He was also a famous teacher; his students included the influential church fathers John Chrysostom and Theodore of Mopsuestia.

His theological career was marked by controversy. While he argued for the full humanity of Christ, his own teachings on the distinction between the divine and human natures of Jesus were later condemned. At the Second Council of Constantinople in 553 CE, he was posthumously declared a forerunner of the heresy known as Nestorianism. Because of this condemnation, almost all of his writings were destroyed. What survives today are only fragments, often preserved in the works of his critics or in later Syriac and Armenian translations. These fragments suggest he wrote biblical commentaries, such as on the Psalms, and polemical treatises against his theological opponents.

According to modern scholars, Diodore’s primary significance lies in his role as a founder of the "School of Antioch." This approach to biblical interpretation emphasized the historical and literal meaning of Scripture, in contrast to the more allegorical method used in Alexandria. His theological ideas, though later condemned, were foundational to major Christological debates and helped shape a distinct and influential tradition of early Christian thought.