The Trinity, from Wiki

The Trinity is a Christian doctrine, stating that God exists as three persons, or in the Greek hypostases, but is one being.[1][2] In other words He is the Triune God. The persons are understood to exist as God the Father, God the Son (incarnate as Jesus Christ), and God the Holy Spirit, each of them having the one identical essence or nature, not merely similar natures. Since the beginning of the third century[3] the doctrine of the Trinity has been stated as "the one God exists in three Persons and one substance, Father, Son, and Holy Spirit."[4] Trinitarianism, belief in the Trinity, is a mark of Oriental and Eastern Orthodoxy, Roman Catholicism and all the mainstream traditions arising from the Protestant Reformation, such as Anglicanism, Lutheranism and Presbyterianism; and the Oxford Dictionary of the Christian Church describes the Trinity as "the central dogma of Christian theology".[4]