Christianity is a global religion centered on the life and teachings of Jesus Christ, who followers believe is the Son of God. It's a monotheistic faith, meaning Christians believe in one God who exists in three co-equal persons: God the Father, God the Son (Jesus Christ), and the Holy Spirit. Christianity is based on the Bible, with the Old Testament and New Testament serving as sacred texts.
Bart Ehrman (born 1955) is an American New Testament scholar focusing on textual criticism of New Testament, historical Jesus, and development of early Christianity. Ehrman has written and edited 30 books, including three college textbooks. He has also authored six New York Times bestsellers. He is currently the James A. Gray Distinguished Professor of Religious Studies at the University of North Carolina at Chapel Hill.
Tertullian (155-240 AD) was a prolific early Christian author from Carthage in the Roman province of Africa. Of Berber origin, he was the first Christian author to produce an extensive corpus of Latin Christian literature. He also was an early Christian apologist and a polemicist against heresy, including contemporary Christian Gnosticism. Tertullian has been called "the father of Latin Christianity" and "the founder of Western theology." Though conservative in his worldview, Tertullian originated new theological concepts and advanced the development of early Church doctrine. He is perhaps most famous for the term trinity (Latin: trinitas). According to The Stanford Encyclopedia of Philosophy, "Tertullian's trinity [is] not a triune God, but rather a triad or group of three, with God as the founding member".
The Christian doctrine of the Trinity (Latin: trinus "threefold") holds that God is one God, but three coeternal consubstantial persons or hypostases. These being the Father, the Son (Jesus Christ), and the Holy Spirit - as "one God in three Divine Persons". The three Persons are distinct, yet are one "substance, essence or nature" (homoousios).