Mark of Ephesus
Our father among the saints Mark of Ephesus (Evgenikos), Pillar of Orthodoxy, was famous for his courageous defense of Orthodoxy at the Council of Florence (1439 A.D.) in spite of the emperor and the pope of Rome. He held Rome to be in schism and heresy for its acceptance of the Filioque clause added to the Nicene-Constantinopolitan Creed and for the claims of the papacy to universal jurisdiction over the Church, and was thus the only Eastern bishop to refuse to sign the decrees of the council.
He died peacefully in the year 1452 A.D. On his death bed, Mark implored Gregory, his disciple, and later Patriarch Gennadius, to be careful of the snares of the West and to defend Orthodoxy.
For his efforts at the Council of Florence and his defense against the addition of the Filioque, the Orthodox Church considers him a saint, calling him a Pillar of Orthodoxy. His feast day is January 19.
"It is impossible to recall peace without dissolving the cause of the schism—the primacy of the Pope exalting himself equal to God." 
"The Latins are not only schismatics but heretics... we did not separate from them for any other reason other than the fact that they are heretics. This is precisely why we must not unite with them unless they dismiss the addition from the Creed filioque and confess the Creed as we do." 
"Our Head, Christ our God... does not tolerate that the bond of love be taken from us entirely." 
"We seek and we pray for our return to that time when, being united, we spoke the same things and there was no schism between us." 
"The Symbol of the Faith must be preserved inviolate, as at its origin. Since all the holy doctors of the Church, all the Councils and all the Scriptures put us on our guard against heterodoxy, how dare I, in spite of these authorities, follow those who urge us to unity in a deceitful semblance of union—those who have corrupted the holy and divine Symbol of Faith and brought in the Son as second cause of the Holy Spirit" (s.v. Jan 19th in The Synaxarion, ed. Hieromonk Makarios of Simonas Petra, and trans. Christopher Hookway; Ormylia: Holy Convent of The Annunciation of Our Lady, 2001).
"The souls of the departed can indeed benefit to their 'advancement,' and even the damned to a relative 'relief' of their lot, thanks to the prayers of the Church and through the infinite mercy of God; but the notion of a punishment prior to the Last Judgment and of a purification through a material fire is altogether foreign to the tradition of the Church" (ibid.).