Who was the king of Rome credited with establishing many Roman religious customs and practices?

Answer: Constantine I

Explanation: Constantine I was the king of Rome who was given the credit of legalizing Christianity and allowing the freedom and practice of other religions through an edict known as The Tolerance of Christianity or edict of Milan, whose enactment was declared in the city from Milan in 313. Constantine signed it in acceptance and with it the persecution that existed against the Christians at that time was ended.