Constantine the Great
Faith: Christian; baptised shortly before his death. His personal religious development and the Christianity of his era are subjects of historical study.
Contribution: Alongside Licinius, he supported the 313 agreement commonly called the Edict of Milan, which established religious toleration and enabled Christian communities to worship openly and recover property. He also supported church building and convened the Council of Nicaea in 325.
Historical context: Constantine's reign was a turning point for Christianity in the Roman Empire, although he did not make Christianity the empire's sole official religion during his lifetime.