How one Roman family's surname became the word for emperor
Caesar began as a family nickname. After Julius Caesar's adopted son took the name and became Rome's first emperor, it hardened into a title for rulers and their heirs, and it survived the empire itself: German speakers turned it into Kaiser, and Slavic languages into Tsar.
The first known Caesar was Sextus Julius Caesar, thought to be the ancestor of the whole line. His great-grandson, the dictator Gaius Julius Caesar, named himself dictator in perpetuity and held that title for only about a month before his assassination in 44 BC. His adopted heir Octavius took the name too, won the civil wars by 30 BC, and in 27 BC became Imperator Caesar Augustus, having dropped his other names but kept Caesar.
A pattern set in. Augustus adopted Tiberius, who became a Caesar on adoption and ruled as Tiberius Caesar Augustus, so the ruling Augustus marked his chosen successor by adopting him and giving him the name. Claudius was the first to claim it without adoption, though he was still family. Galba, who seized power when Nero died in AD 68, had no family claim at all, and from then on Caesar was clearly a title rather than a surname. Vespasian made it part of the imperial formula when he founded the Flavian dynasty in AD 69, and under Antoninus Pius the standard pattern became Imperator Caesar, the ruler's name, then Augustus.
On its own, caesar came to mean heir. Soldier-emperors during the chaos of the third century handed it to their sons to shore up legitimacy, with little success: almost all were killed before or with their fathers. In 293 Diocletian's Tetrarchy made two caesars junior partners of two senior augusti. Constantine used it as a ceremonial honour for young heirs, and the last Western holder was Palladius, son of Petronius Maximus, in 455.
In Byzantium, kaisar lived on as a top court rank, increasingly given to younger sons and powerful relatives, and once, by Justinian II, to the Bulgarian khan Tervel for helping him regain his throne in 705. New titles created by Alexios I and Manuel I pushed it down to fourth place. Late Byzantine caesars wore a red and gold hat, a red tunic like the emperor's, and blue shoes and stockings.
Source: Caesar (title)
