Who is known as "Constantine the Great" and ruled from 306 to 337?

Constantine the Great, who ruled from 306 to 337 AD, is primarily recognized as the Emperor of Rome. He is a pivotal figure in history due to his significant contributions to the Roman Empire, particularly in relation to his role in the establishment of Christianity as a major religion within the empire. Under his reign, he enacted the Edict of Milan in 313, which granted religious tolerance to Christians and allowed for the faith to be practiced openly.

Additionally, Constantine is known for founding the city of Constantinople, which later became the capital of the Byzantine Empire. His leadership and reforms laid the groundwork for the transition of the Roman Empire from paganism to Christianity, making his moniker "the Great" particularly fitting. The other options do not accurately reflect his primary identity or accomplishments, as they refer to different figures or aspects of church leadership.