Emperor John may refer to:
Roman and Byzantine emperors
Joannes (died 425), augustus of the Western Roman Empire, 423-425
Byzantine emperors
John I Tzimiskes, (circa 925–976), Byzantine Emperor from 969 to 976
John II Komnenos, Byzantine emperor
John III Doukas Vatatzes, Byzantine emperor
John IV Laskaris, Byzantine emperor
John V Palaiologos, Byzantine emperor
John VI Kantakouzenos, Byzantine emperor
John VII Palaiologos, Byzantine emperor
John VIII Palaiologos, Byzantine emperor
Latin emperors
John of Brienne, Latin Emperor of Constantinople
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