Arian controversy in the context of "Pope Sylvester I"

Hosius of Corduba (c. 256–359), also known as Hosius the Confessor, Osius or Ossius, was a bishop of Corduba (now Córdoba, Spain) and an important and prominent advocate for Homoousion Christianity during the period when the Arian controversy divided early Christianity.

He probably presided at the First Council of Nicaea and also presided at the Council of Serdica.

The Patriarch of Antioch was the head of the Church of Antioch. According to tradition, the bishopric of Antioch was established by Saint Peter in the 1st century AD and was later elevated to the status of patriarchate by the First Council of Nicaea in 325. The church first underwent schism after the deposition of Eustathius in 330 over the issue of the Arian controversy and persisted until its resolution in 414.

After the Council of Chalcedon of 451, the church suffered division until the deposition of Patriarch Severus of Antioch in 518 resulted in a permanent schism from which two separate lines of patriarchs emerged. The Non-Chalcedonian supporters of Severus went on to form what is now known as the Syriac Orthodox Church, whilst the Chalcedonians developed the church now known as the Greek Orthodox Church of Antioch.

Tomus ad Antiochenos is a letter or mediation proposal written by Bishop Athanasius of Alexandria on behalf of a regional synod he convened in Alexandria in 362, addressed to a group of bishops seeking a solution to the schism between "Eustathians" and "Meletians" in the parishes of Antioch. This letter played a key role in the Trinitarian theological debates between the one-hypostasis model and the three-hypostasis model of the Trinity, anticipating the turning point in this question from the 370s onward.

The central concern is to achieve theological agreement based on the Nicene Creed. By recognizing that certain theological points of contention in the Arian controversy were based not only on differences of belief, but also on different language rules or conceptual differences between Latin and Greek, the Tomus paved the way for the Trinitarian theological language rules of the three Cappadocians from the 370s onward: Basil of Caesarea, his brother Gregory of Nyssa, and their mutual friend Gregory of Nazianzus subsequently established the concept of the one being (Ousia) and the three hypostases of God, which became binding with the decision of the First Council of Constantinople in 381.

Acacius of Caesarea (Greek: Ἀκάκιος; date of birth unknown, died in 366) was a Christian bishop probably originating from Syria; Acacius was the pupil and biographer of Eusebius and his successor on the see of Caesarea Palestina. Acacius is remembered chiefly for his bitter opposition to Cyril of Jerusalem and for the part he was afterwards enabled to play in the more acute stages of the Arian controversy. The Acacian theological movement is named after him. In the twenty-first oration of St. Gregory Nazianzen, the author speaks of Acacius as being "the tongue of the Arians".

Ulfilas (Ancient Greek: Οὐλφίλας; c. 311 – 383), known also as Wulfila(s) or Urphilas, was a 4th-century Gothic preacher of Cappadocian Greek descent. He was the apostle to the Gothic people.

Ulfila served as a bishop and missionary, participated in the Arian controversy, and is credited with converting the Goths to Christianity as well as overseeing translation of the Bible into the Gothic language. For the purpose of the translation he developed the Gothic alphabet, largely based on the Greek alphabet, as well as Latin and Runic characters. Although the translation of the text into Gothic has traditionally been ascribed to Ulfila, analysis of the text of the Gothic Bible indicates the involvement of a team of translators, possibly under his supervision.