John of Dailam was a 7th-century East Syriac monk who established multiple monasteries across Persia and Mesopotamia. Born in 660 in Hdatta, near the junction of the Tigris and Upper Zab rivers, he entered the monastery of Bēṯ ʿĀbē during his youth. After being captured by the Dailamites during conflicts with Arab forces, he escaped his captors and traveled to the Caspian Sea region to preach the Christian faith to the local population.