Saint Metrophanes, the first Patriarch of Constantinople, was born to pagan parents but converted to Christianity at a young age. His father, Dometius, was a brother of the Roman emperor Probus and fled Rome as a Christian during a time of persecution. After Dometius became Bishop of Byzantium, Metrophanes succeeded him in 316 AD.
Emperor Constantine the Great admired the holiness and wisdom of Saint Metrophanes and brought him to Rome before transferring the capital to Byzantium. At the First Ecumenical Council in 325 AD, Metrophanes, then 117 years old, appointed his delegate Alexander to represent him. The Council bestowed upon him the title of Patriarch.
Saint Metrophanes passed away soon after the Council, predicting Alexander of Alexandria as his successor and praising the future Saint Athanasius. His relics are enshrined in a church in Constantinople.
It is important to note that the Canons to the Holy Trinity in the Midnight Office in the Octoechos were not authored by this Metrophanes, but by Bishop Metrophanes of Smyrna in the ninth century.
Saint Metrophanes lived at the end of Roman persecution of Christians and played a significant role in the establishment of Byzantium as the new capital. His appointment of successors and prophecies regarding future leaders of the Church show his deep spiritual insight and devotion to Christ.
Source: oca.org / goarch.org / westserbdio.org