Tertullian

Tertullian was a Carthaginian lawyer and convert to Christianity who became the first major Christian writer in Latin, coining much of the Latin theological vocabulary the Western Church would use for centuries, including trinitas ("Trinity") and sacramentum ("sacrament"). He wrote On Repentance during his orthodox, pre-Montanist period; later in life he broke from the mainstream Church to join the rigorist Montanist movement, so his later writings are read with more caution than his earlier ones, and he is not venerated as a saint.