Final answer:
Constantine was the first Christian emperor of Rome, marking a significant era in Roman history with his conversion to Christianity and his support for the Christian faith.
Step-by-step explanation:
The individual who became the first Christian emperor of Rome was Constantine. His reign, starting when his father's troops proclaimed him Augustus in Eboracum (York, England) in 306 CE, marked significant changes in the history of Rome, especially in the realm of religion. Constantine, after a vision he claimed was sent by the Christian God before his victory at the Battle of Milvian Bridge in 312 CE, converted to Christianity and set a precedent for supporting Christian institutions and empowering Christian officials.
Despite facing opposition against figures like Maxentius, Constantine was officially recognized by Galerius, the ruler of the Eastern provinces of the Roman Empire. His contributions to the Christian faith during his rule had a lasting impact, establishing an era where rulers of Rome were explicitly Christian, and eventually moving the capital from Rome to Constantinople. The importance of Constantine in Christianity and as a Roman Emperor is undeniable, as his leadership bridged the gap between the older pagan traditions and the Christian governance that would come to define the empire's future.