The correct answer is Constantine.
The Roman Empire had a politeistic cult. Among their many gods some can be highlighted such as Jupiter, Neptuno, Mars, Minerva or Venus. When Christianity emerged in the Middle East and arrived to the territories of the Roman Empire, its emisaries and followers suffered intense persecution by the authorities.
During the ruling of emperor Constantine I, the Edict of Milan was enacted in 313 to declare religious tolerance, and it actually worked as an instrument for the legalization of Christianity. Constantine I became the first emperor that converted to Christianism.