<P> In like manner also the three days which were before the luminaries, are types of the Trinity (Τριάδος), of God, and His Word, and His wisdom . And the fourth is the type of man, who needs light, that so there may be God, the Word, wisdom, man . </P> <P> Tertullian, a Latin theologian who wrote in the early 3rd century, is credited as being the first to use the Latin words "Trinity", "person" and "substance" to explain that the Father, Son, and Holy Spirit are "one in essence--not one in Person". </P> <P> The Ante - Nicene Fathers asserted Christ's deity and spoke of "Father, Son and Holy Spirit", even though their language is not that of the traditional doctrine as formalised in the fourth century . Trinitarians view these as elements of the codified doctrine . Ignatius of Antioch provides early support for the Trinity around 110, exhorting obedience to "Christ, and to the Father, and to the Spirit". Justin Martyr (AD 100--c. 165) also writes, "in the name of God, the Father and Lord of the universe, and of our Saviour Jesus Christ, and of the Holy Spirit". The first of the early church fathers to be recorded using the word "Trinity" was Theophilus of Antioch writing in the late 2nd century . He defines the Trinity as God, His Word (Logos) and His Wisdom (Sophia) in the context of a discussion of the first three days of creation . The first defence of the doctrine of the Trinity was in the early 3rd century by the early church father Tertullian . He explicitly defined the Trinity as Father, Son, and Holy Spirit and defended the Trinitarian theology against the "Praxean" heresy . St. Justin and Clement of Alexandra used the Trinity in their doxologies and St. Basil likewise, in the evening lighting of lamps . </P> <P> Another early, and already more philosophic, formulation of the Trinity (again without usage of that term) is attributed to the Gnostic teacher Valentinus (lived c. 100--c. 160), who according to the fourth century theologian Marcellus of Ancyra, was "the first to devise the notion of three subsistent entities (hypostases), in a work that he entitled On the Three Natures ." The highly allegorical exegesis of the Valentinian school inclined it to interpret the relevant scriptural passages as affirming a Divinity that, in some manner, is threefold . The Valentinian Gospel of Philip, which dates to approximately the time of Tertullian, upholds the Trinitarian formula . Whatever his influence on the later fully formed doctrine may have been, however, Valentinus's school is rejected as heretical by orthodox Christians . </P>

Who first held that the trinity is defined as one substance in three persons