Final answer:
Constantine was the Roman Emperor who inaugurated the process of the Christianization of the Roman Empire by ending the persecution of Christians and becoming a patron of the Church.
Step-by-step explanation:
The Roman Emperor who inaugurated the process of the Christianization of the Roman Empire was Constantine. Constantine's decision to cease the persecution of Christians and his imperial sanction of Christianity transformed its status and nature. He became a great patron of the Church and set a precedent for the position of the Christian emperor within the Church.