Loukas Notaras (Greek: Λουκᾶς Νοταρᾶς) (executed 3–4 June 1453) was the last Megas Doux of the Byzantine Empire. This position (literally Grand Duke, but more appropriately Lord High Admiral) had been expanded under the late Palaiologid emperors and functioned as an unofficial Prime Minister, overseeing the Imperial Bureaucracy in place of the Megas Logothetes who had previously exercised this function.