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