Hilario Doria (Greek: 'Ιλαρíων Tóρια, romanized: Hilarion Toria,[1] Latin: Illarius Doria;[1] died c. 1424) was a Byzantine court official, diplomat and translator of Genoese descent. Doria became influential in the reign of Emperor Manuel II Palaiologos (r. 1391–1425) through marrying the emperor's half-sister Zampia Palaiologina and was appointed as mesazon, one of the highest positions in the imperial administration. Doria had a distinguished career as a Byzantine diplomat in Western Europe; he worked with Pope Boniface IX on (ultimately unsuccessful) plans for organising a crusade and visited Richard II of England, who might have conferred a knighthood on him. Doria's career came to an end in 1423 when he was caught conspiring with Manuel's son Demetrios Palaiologos; Doria, Demetrios and their associates soon thereafter fled to Hungary, where Doria shortly thereafter died.