Constantine the Great 25 July 306 AD – 29 October 312 AD (Caesar in the west; self-proclaimed Augustus from 309; recognized as such in the east in April 310.) 29 October 312 – 19 September 324 (Undisputed Augustus in the west, senior Augustus in the empire.) 19 September 324 – 22 May 337 (As emperor of whole empire.) (jul 25, 306 – oct 29, 337)

Description:

Constantine was the first Roman emperor to convert to Christianity.
He played an influential role in the proclamation of the Edict of Milan in 313, which declared religious tolerance for Christianity in the Roman empire.

Added to timeline:

Date: