For today’s saint we have Saint Eulogius:
Saint Eulogius of Alexandria (Greek: Εὐλόγιος) was Greek Patriarch of that see (Eulogius I) from 580 to 608. He is regarded as a saint, with a feast day of September 13.
He was a successful combatant of the heretical errors then current in Egypt, notably the various phases of Monophysitism. He was a warm friend of Pope St. Gregory the Great, who corresponded with him, and received from that pope many flattering expressions of esteem and admiration.
St. Eulogius refuted the Novatians, some communities of which ancient sect still existed in his diocese, and vindicated the hypostatic union of the two natures in Christ, against both Nestorius and Eutyches. Cardinal Baronius says that Gregory wished Eulogius to survive him, recognizing in him the voice of truth.
It has been said that he restored for a brief period to the Church of Alexandria life and youthful vigour.
Besides the above works and a commentary against various sects of Monophysites (Severians, Theodosians, Cainites and Acephali) he left eleven discourses in defence of Pope Leo I and the Council of Chalcedon, also a work against the Agnoetae, submitted by him before publication to Pope Gregory I, who after some observations authorized it unchanged. With exception of one sermon and a few fragments, all the writings of St. Eulogius have perished.
(All quoted from the wiki on him)