Trinitarianism

Trintarianism is the Christian concept of ‘Three persons, one substance’ or in Latin ‘Tres personae, una Substantia’, called the ‘Trinity’.
A Trinitarian upholds that there is only one God, and that he is united in three Natures or three Persons comprising God the Father, God the Son and God the Holy Spirit.

Trinitarianism was first advocated by Tertullian (160-225 CE).
Trinitarianism was adopted by the Christian Church at the First Ecumenical Council, the First Council of Nicaea in 325 CE, when it rejected Arianism.
Arianism was eventually banned in 381 CE at the First Council of Constantinople.
The main defender of Trinitarianism was Athanaeus, Bishop of Alexandria between 328-373 CE.