[2][3] Sextus's great-grandson was the dictator Gaius Julius Caesar, who seized control of the Roman Republic following his war against the Senate.

[4] Eventually, distrust and jealousy between the triumvirs led to a lengthy civil war which ultimately ended with Octavius gaining control of the entire Roman world in 30 BC.

He had previously dropped all his names except for "Caesar", which he treated as a nomen, and had adopted the victory title imperator ("commander") as a new praenomen.

The precedent was thus then set: the Emperor, styled as "Augustus", designated his successor by adopting him and giving him the name "Caesar".

However, he was at least a member of the Julio-Claudian dynasty, being the maternal great-nephew of Augustus on his mother's side, the nephew of Tiberius, and the uncle of Caligula (who was also called "Gaius Julius Caesar").

The sole caesar to successfully obtain the rank of augustus and rule for some time in his own right was Gordian III, and even he was heavily controlled by his court.

After Julian's revolt of 360, the title fell out of imperial fashion for some time, with emperors preferring simply to elevate their sons directly to augustus, starting with Gratian in 367.

Hence the title was more frequently awarded to second- and third-born sons, or to close and influential relatives of the Emperor: for example, Alexios Mosele who was the son-in-law of Theophilos (ruled 829–842), Bardas who was the uncle and chief minister of Michael III (r. 842–867), and Nikephoros II (r. 963–969) who awarded the title to his father, Bardas Phokas.

[11][12] An exceptional case was the conferment of the dignity and its insignia to the Bulgarian khan Tervel by Justinian II (r. 685–695, 705–711) who had helped him regain his throne in 705.

In the Palaiologan period, it was held by prominent nobles such as Alexios Strategopoulos, but from the 14th century, it was mostly awarded to rulers of the Balkans such as the princes of Vlachia, Serbia and Thessaly.

[12] In the late Byzantine hierarchy, as recorded in the mid-14th century Book of Offices of pseudo-Kodinos, the rank continued to come after the sebastokratōr.

Pseudo-Kodinos further records that the caesar was equal in precedence to the panhypersebastos, another creation of Alexios I, but that Emperor Michael VIII Palaiologos (r. 1259–1282) had raised his nephew Michael Tarchaneiotes to the rank of protovestiarios and decreed that to come after the caesar; while under Andronikos II Palaiologos (r. 1282–1328) the megas domestikos was raised to the same eminence, when it was awarded to the future emperor John VI Kantakouzenos (r.

[16] According to pseudo-Kodinos, the caesar's insignia under the Palaiologoi was a skiadion hat in red and gold, decorated with gold-wire embroideries, with a veil bearing the wearer's name and pendants identical to those of the despotēs and the sebastokratōr.

He wore a red tunic (rouchon) similar to the emperor's (without certain decorations), and his shoes and stockings were blue, as were the accouterments of his horse; these were all identical to those of the sebastokratōr, but without the embroidered eagles of the latter.

After the Fall of Constantinople, having conquered the Byzantine Empire, Mehmed took the title Kayser-i Rûm, claiming succession to the Roman imperium.

[22] Gennadius II, a staunch antagonist of the West because of the Sack of Constantinople committed by the Western Catholics and theological controversies between the two Churches, had been enthroned the Ecumenical Patriarch of Constantinople-New Rome with all the ceremonial elements and ethnarch (or milletbashi) status by the Sultan himself in 1454.

[24] Ottoman sultans were not the only rulers to claim such a title, as there was the Holy Roman Empire in Western Europe, whose emperor, Frederick III, traced his titular lineage from Charlemagne who obtained the title of Roman Emperor when he was crowned by Pope Leo III in 800, although he was never recognized as such by the Byzantine Empire.

The Russians, who defined Moscow as the Third Rome, were similarly sanctioned by the Ottomans, who ordered the Crimean Khanate to raid Russia on numerous occasions.