Emperor John may refer to:
Roman emperors Joannes (died 425), Western emperor but not recognized by the East
Eastern (Byzantine) emperors John I Tzimiskes John II Komnenos John III Doukas Vatatzes, in exile John IV Laskaris, in exile John V Palaiologos John VI Kantakouzenos John VII Palaiologos John VIII Palaiologos
Latin emperors John of Brienne
Emperors at Trebizond John I of Trebizond, Emperor of Trebizond from 1235 to 1238 John II of Trebizond (c. 1262–August 16, 1297), Emperor of Trebizond from 1280 to 1297 John III of Trebizond (c. 1321–1362), Emperor of Trebizond John IV of Trebizond (c. 1403–1459), Emperor of Trebizond from 1429 to 1459
Ethiopian emperors Yohannes I of Ethiopia, Emperor of Ethiopia Yohannes II of Ethiopia, Emperor of Ethiopia Yohannes III of Ethiopia, Emperor of Ethiopia Yohannes IV of Ethiopia, Emperor of Ethiopia
Russian emperors Ivan I of Russia, Ivan Danilovich Kalita; numbered with Tsars of Russia but not an emperor Ivan II of Russia, Ivan Ivanovich; numbered with Tsars of Russia but not an emperor Ivan III of Russia, Ivan Vasilevich; numbered with Tsars of Russia but not an emperor Ivan IV of Russia, Ivan Vasilevich, Ivan the Terrible, Tsar of Russia Ivan V of Russia, Ivan Alekseievich, Tsar of Russia Ivan VI of Russia, Ivan Antonovich, Emperor of Russia
Bulgarian emperors Ivan Vladislav of Bulgaria, Emperor of Bulgaria Ivan Asen I, Emperor of Bulgaria Ivan Asen II, Emperor of Bulgaria Ivan Asen III, Emperor of Bulgaria Ivan Stephen of Bulgaria, Emperor of Bulgaria Ivan Alexander of Bulgaria, Emperor of Bulgaria Ivan Shishman of Bulgaria, Emperor of Bulgaria Ivan Sratsimir of Bulgaria, Emperor of Bulgaria