Theodoret of Cyrus was a Christian bishop, theologian, and historian of the 5th century CE. He was born around 393 CE in Antioch and served as the Bishop of Cyrrhus in Syria from 423 CE until his death, traditionally dated to around 460 CE. He was a highly educated figure, trained in classical Greek literature and philosophy as well as Christian scripture.

His long career was dominated by major theological debates of his time. Theodoret was a leading defender of the Antiochene theological tradition, which emphasized a clear distinction between the divine and human natures of Christ. This stance placed him at the center of controversy. He opposed the teachings of Cyril of Alexandria and initially supported Nestorius, which led to his condemnation and deposition at a council in 449 CE. He was later reinstated at the Council of Chalcedon in 451 CE after distancing himself from Nestorius, though some suspicion around his writings persisted.

Theodoret was a prolific author whose surviving works provide a vital window into his era. His Ecclesiastical History continues the narrative of the early church into the 5th century. The History of the Monks of Syria offers important biographies of contemporary ascetics. Among his doctrinal works, the dialogue Eranistes was instrumental in shaping the Christological language of the Council of Chalcedon. He also wrote extensive biblical commentaries, a treatise against paganism titled Cure of Hellenic Maladies, and a large collection of letters.

Modern scholars regard Theodoret as a significant intellectual figure. His historical works are crucial primary sources, his biblical commentaries exemplify the Antiochene school of interpretation, and his theological arguments were central to defining orthodox Christian doctrine in the late antique period.