Demetrios Kydones, Latinized as Demetrius Cydones or Demetrius Cydonius (Greek: Δημήτριος Κυδώνης; 1324 in Thessalonica - 1398 in Crete), was a Byzantine theologian, translator, writer and influential statesman, who served an unprecedented three terms as Mesazon (Imperial Prime Minister or Chancellor) of the Byzantine Empire under three successive emperors: John VI Kantakouzenos, John V Palaiologos and Manuel II Palaiologos.
As Imperial Premier, Kydones' West-Politik effort during his second and third stints was to bring about a reconciliation of the Byzantine and Roman Churches, in order to cement a military alliance against the ever-encroaching Islam, a program that culminated in Emperor John V Palaiologos' reconciliation with Catholicism.
His younger brother and somewhat-collaborator in his efforts was the noted anti-Palamite theologian Prochoros Kydones.
Read more about Demetrios Kydones: Against The Greek Schism