Eusebius of Caesarea was a Christian historian and bishop who lived during the early 4th century. He is best known for his work, the "Ecclesiastical History," which chronicles the development of the Christian church from the time of Jesus Christ to his own era. Eusebius is often referred to as the "Father of Church History" for his detailed accounts and efforts to document the lives of early Christian leaders. In addition to his historical writings, Eusebius played a significant role in the early church's relationship with the Roman Empire. He was a supporter of Constantine the Great, the first Roman emperor to convert to Christianity, and he helped to promote the faith during a time of significant change and growth for Christianity.