Note: It is difficult to determine when exactly the Roman Empire ends and the Byzantine Empire begins; Diocletian split the Roman Empire into eastern and western halves for administrative purposes in 284. Candidates for the "first" Byzantine emperor include Constantine I (the first Christian emperor, who moved the capital to Constantinople), Valens (the Battle of Adrianople (378) provides one of the traditional cut-off events to mark the start of the medieval period), Arcadius (treating Theodosius I as the last emperor of a single Roman Empire), and Zeno I (as the last western emperor Romulus Augustus was deposed during his reign). Others date the beginning of the Empire even as late as Heraclius (who replaced the traditional Roman imperial title of "Augustus" with "Basileus", the Greek word for "Emperor", and discontinued the use of Latin by making Greek the official language). Numismatists note the monetary reforms of Anastasius I in 498, which used the Greek numbering system. Of course, the Byzantines themselves continued to think of their empire as "Roman" for over a millennium.
Julian the Apostate (331 - 363, ruled 361 - 363) – son in-law of Constantine I, brother-in-law and first cousin of Constantius II, grandson of Constantius I
Justinian I the Great (482-565, ruled 527 - 565) – nephew of Justin I
Justin II (520-578, ruled 565 - 578) – nephew of Justinian I
Tiberius II Constantine (540-582, ruled 578 - 582) – father-in-law of a grand-nephew of Justin I; Count of the Excubitors under Justin II; adopted by Justin II in 574
Maurice I Tiberius (539-602, ruled 582 - 602) – son-in-law of Tiberius II
Non-dynastic
Phocas the Tyrant (???-610, ruled 602 - 610) – overthrew Maurice
Andronicus I Comnenus (1118-1185, ruled 1183 - 1185) – grandson of Alexius I; nephew of John II; first cousin once removed of Alexius II; married Alexius II's widow
Constantine XI Palaeologus (1405-1453, ruled 1449 - 1453) – son of Manuel II, brother of John VIII
In 1453 Mehmed II overthrew the Byzantine Empire and claimed the title of Caesar; his successors continued this claim. See Osmanli for the complete list of Ottoman sultans.
Roman Empire is also used as translation of the expression Imperium Romanum, probably the best known Latin expression where the word "imperium" is used in the meaning of a territory, the "Roman Empire", as that part of the world where Rome ruled.
Roman titles of power were adopted by successor states and other entities with imperial pretensions, including the Frankish kingdom, the Holy Roman Empire, the first and second Bulgarian empires, the Russian/Kiev dynasties, and the German Empire.
The Holy Roman Empire, an attempt to resurrect the Empire in the West, was established in 800 when Pope Leo III crowned Charlemagne as RomanEmperor on Christmas Day, though the empire and the imperial office did not become formalized for some decades.
The forced suicide of emperor Nero, in 68, was followed by a brief period of civil war (the first Roman civil war since Antony's death in 31 BC) known as the year of the four emperors.
The emperors of this period were Nerva (96–98), Trajan (98–117), Hadrian (117–138), Antoninus Pius (138–161) and Marcus Aurelius (161–180), each being adopted by his predecessor as his successor during the former's lifetime.
The Western Roman Empire was divided among the eldest son Constantine II and the youngest son Constans.