Trinitarian in the context of "God the Holy Spirit"

Odoacer (c. 433 – 15 March 493 AD), also spelled Odovacer or Odovacar, was a barbarian soldier and statesman from the Middle Danube who was an officer of the Roman army and deposed the Western Roman child emperor Romulus Augustulus to become the ruler of Italy (476–493). Odoacer's overthrow of Romulus Augustulus is traditionally understood as marking the end of the Western Roman Empire.

Although he ruled Italy, Odoacer styled himself a client of the Eastern emperor Zeno in Constantinople. He was addressed not only as Latin: rex but also as dux and patrician, the latter title granted by Zeno. In the sole surviving document from his chancery—and by the consul Basilius—Odoacer used the title of king. Backed by the Roman Senate, he distributed land with little resistance. Soldier unrest in 477–478 caused violence, but his later reign was stable. Though an Arian, he seldom interfered in the Trinitarian state church.

Homoousion (/ˌhɒmoʊˈuːsiɒn, ˌhoʊm-/ HO(H)M-oh-OO-see-on; Ancient Greek: ὁμοούσιον, lit. 'same in being, same in essence', from ὁμός, homós, "same" and οὐσία, ousía, "being" or "essence") is a Christian theological term, most notably used in the Nicene Creed for describing Jesus (God the Son) as "same in being" or "same in essence" with God the Father (ὁμοούσιον τῷ Πατρί). The same term is also applied to the Holy Spirit in order to designate him as being "same in essence" with the Father and the Son. Those notions became cornerstones of theology in Nicene Christianity, and also represent one of the most important theological concepts within the Trinitarian doctrinal understanding of God.

Gregory of Nazianzus (Greek: Γρηγόριος ὁ Ναζιανζηνός, romanized: Grēgorios ho Nazianzēnos; c. 329 – 25 January 390), also known as Gregory the Theologian or Gregory Nazianzen, was an early Roman Christian theologian and prelate who served as Archbishop of Constantinople from 380 to 381. He is widely considered the most accomplished rhetorical stylist of the patristic age. As a classically trained orator and philosopher, he infused Hellenism into the early Church, establishing the paradigm of Byzantine theologians and church officials.

Gregory made a significant impact on the shape of Trinitarian theology among both Greek and Latin-speaking theologians, and he is remembered as the "Trinitarian Theologian". Much of his theological work continues to influence modern theologians, especially in regard to the relationship among the three Persons of the Trinity. Along with the brothers Basil of Caesarea and Gregory of Nyssa, he is known as one of the Cappadocian Fathers.

The Breviary of Alaric (Breviarium Alaricianum or Lex Romana Visigothorum) is a collection of Roman law, compiled by Roman jurists and issued by referendary Anianus on the order of Alaric II, King of the Visigoths, with the approval of his bishops and nobles. It was promulgated on 2 February 506, the 22nd year of his reign. It applied, not to the Visigothic nobles who lived under their own law, which had been formulated by Euric, but to the Hispano-Roman and Gallo-Roman population, living under Visigoth rule south of the Loire and, in Book 16, to the members of the trinitarian Catholic Church; the Visigoths were Arian and maintained their own clergy.

The Arian controversy was a series of Christian disputes about the nature of Christ that began with a dispute between Arius and Athanasius of Alexandria, two Christian theologians from Alexandria, Egypt. The most important of these controversies concerned the relationship between the substance of God the Father and the substance of His Son. The position advanced initially by Arius argued that the Son of God came after God the Father in both time and substance. This conflicted with the Trinitarian faction initially advanced by Athanasius which argued that the Christ was coeternal and consubstantial with God the Father.

Emperor Constantine, through the Council of Nicaea in 325, attempted to unite Christianity and establish a single, imperially approved version of the faith. Ironically, his efforts were the cause of the deep divisions created by the disputes after Nicaea.