Tertullian

Tertullian (c. 155–220) was the first great theologian to write in Latin, coining the terms trinitas, substantia, and persona that shaped Trinitarian theology. Born in Carthage, he championed orthodoxy against Marcion, Praxeas, and the philosophers. His Apology defended Christianity before Roman courts, while Against Marcion (Books IV–V) provides the earliest extended verse-by-verse engagement with Luke’s Gospel and the Pauline letters, refuting Marcion’s dualist canon.

Tertullian gave Latin theology its very vocabulary, coining trinitas, substantia, and persona to speak of the one God in three persons. A relentless controversialist, he argued from Scripture against Marcion's rejection of the Old Testament and against Praxeas's confusion of the persons, defending both the goodness of the Creator and the distinct reality of Father, Son, and Spirit. Though he ended his life among the rigorist Montanists, his formulations passed permanently into the church's confession.