Tertullian

Tertullian of Carthage was the first major Christian theologian to write in Latin, and he shaped the language the Western Church still uses — he was the earliest writer known to call God a trinitas, a “Trinity.” His Apology answered the pagan charges laid against Christians, while treatises such as Against Praxeas and the Prescription Against Heretics defended and defined Latin doctrine. Drawn in later life to the rigorist Montanist movement, he was never canonized — yet his influence on Western Christianity is hard to overstate.