Augustine of Hippo (354-430), one of the greatest Christian thinkers of all time, largely responsible for the doctrines of the Trinity, original sin, creation, the sacraments, and the Church as they were developed in the Latin West. Most famous for his Confessions, an autobiographical account of his conversion from Manichaeism to Christianity, and On the City of God, a sweeping attempt to explain all of human history as a conflict between the City of God and the City of Man.
Peter Lombard (c. 1096-1164), master at the cathedral school and bishop of Paris, author of commentaries on the Psalms and the letters of Paul. Most famous for his Sentences, upon which the late medieval discipline of theology was built. The Sentences are divided into four books covering questions about the Trinity, creation, the Incarnation of the Word, and the sacraments. All four books consist largely of quotations from Augustine.