Flavius Valerius Aurelius Constantinus Augustus also known as Constantine the Great was born 27th of February 272 AD. He ruled as a Roman Emperor from 306 to 337 AD. His father became the Caesar in the west in 293 AD. Constantine was sent to the east and rose in his ranks in the military.
His father became the “Augustus” (the highest ranking ruler in the west) and then died a year later in 306 AD. Constantine was next to take is place but was not wanted by others. This resulted in some civil wars.
The most noted was the battle at Milvian Bridge. The night before the battle Constantine had a vision to mark the symbol of a cross on his shield. He recognized it to be the symbol the Christians used and was covered after this event. Constantine did win the battles and became emperor of Rome which he once again united.
As a result of his conversion he created the Edict of Milan which decreed tolerance for Christianity in the empire. This passed in 313 AD but had to be frequently enforced. This must have been the favorable Emperor for the Christian people.