Qaisar (Arabic: قيصر), also spelled Qaysar, is the Arabic version of the name Caesar and it is used as a given name in Arabia and the Islamic world. The word 'Caesar' derives from the cognomen of the Roman dictator Julius Caesar. The Roman and later Byzantine, or Eastern Roman, emperors were called Qaisar-e-Rum (Caesar of Rome) by the Arabs and Persians. The Ottoman Sultan Fâtih Sultan Mehmed also took the title Kayser-i Rum (Caesar of Rome, meaning the Eastern Roman Empire) after conquering Constantinople, modern Istanbul, on May 29, 1453.
https://en.wikipedia.org/wiki/Qaisar