Feast of Basil the Great, Gregory the Theologian, and John Chrysostom.
The feast of the Three Holy Hierarchs honors together Sts. Basil the Great, Gregory the Theologian, and John Chrysostom, the great fathers and ecumenical teachers of the Church. According to tradition, the common feast was established in the eleventh century after disputes arose in Constantinople over which of the three was greatest; the hierarchs made known in a vision that they are one before God, and a shared commemoration was appointed.
Together they represent the harmony of theology, eloquence, and pastoral care. In Greece the day is also kept as the feast of education and letters, the patronal celebration of schools, teachers, and students.
Feast day
On the New Calendar, Three Holy Hierarchs is commemorated on January 30. Churches on the Old (Julian) Calendar keep the feast on February 12 of the civil calendar.
Who celebrates a name day
People with these names keep their name day on this feast:
Basil, Gregory, John, Vasilis, Grigoris, Giannis
Also commemorated on January 30

Chryse the Martyr
Holy Woman, Χρυσή
Holy Virgin Martyr Chryse of Rome, who suffered with St. Hippolytos.
Kensourinos and Sabinos
Martyr, Κενσουρίνος και Σαβαΐνος
Holy Martyrs Kensourinos and Sabinos, who suffered with St. Hippolytos at Ostia.
Theophilos the New
Martyr, Θεόφιλος ο Νέος
Holy Martyr Theophilos the New, a Byzantine commander martyred by the Arabs.
Finding of the Icon of the Annunciation in Tinos
Saint, Ευαγγελίστρια Τήνου
Commemoration of the finding of the wonderworking icon of the Annunciation on Tinos.
Icon: public domain image from Wikimedia Commons.