Caesar (plural Caesars; Latin: Caesar, plural: Caesares) is a title of imperial character. It derives from the cognomen of Julius Caesar, the Roman dictator. The change from being a familial name to a title adopted by the Roman Emperors can be dated to about AD 68/69, the so-called "Year of the Four Emperors".

Although the etymology of the name of Julius Caesar is not known with certainty, many scholars believe that it was simply a use of the Latin expression caesar meaning hairy. The Julii Caesares were a specific branch of the gens Julia. The first known bearer of the name was one Numerius Julius Caesar (born before 300 BC), who might have been conspicuous for having a fine head of hair (alternatively, given the Roman sense of humour and Julius Caesar's own receding hairline, it could be that the family branch was conspicuous for going bald). It is probably^{[Is this a fact or an opinion?]} not related to the root "to cut", a hypothesized etymology for Caesarian section^{[citation needed]}.

The first Emperor, Caesar Augustus, bore the name as a matter of course; born Gaius Octavius, he was posthumously adopted by Caesar in his will, and per Roman naming conventions was renamed "Gaius Julius Caesar Octavianus" (usually called "Octavian" in English when referring to this stage of his life).

Caesar or Cæsar may refer to:

Gaius Julius Caesar (Classical Latin: [ˈɡaː.i.ʊs ˈjuː.lɪ.ʊs ˈkaj.sar], July 100 BC – 15 March 44 BC) was a Roman general and statesman and a distinguished writer of Latin prose. He played a critical role in the gradual transformation of the Roman Republic into the Roman Empire.

In 60 BC, Caesar, Crassus and Pompey formed a political alliance that was to dominate Roman politics for several years. Their attempts to amass power through populist tactics were opposed by the conservative elite within the Roman Senate^{[citation needed]}, among them Cato the Younger with the frequent support of Cicero. Caesar's conquest of Gaul, completed by 51 BC, extended Rome's territory to the English Channel and the Rhine. Caesar became the first Roman general to cross both when he built a bridge across the Rhine and conducted the first invasion of Britain.

These achievements granted him unmatched military power and threatened to eclipse Pompey's standing. The balance of power was further upset by the death of Crassus in 53 BC. Political realignments in Rome finally led to a standoff between Caesar and Pompey, the latter having taken up the cause of the Senate. Ordered by the Senate to stand trial in Rome for various charges, Caesar marched on Rome with one legion—legio XIII—from Gaul to Italy, crossing the Rubicon in 49 BC. This sparked a civil war from which he emerged as the unrivaled leader of the Roman world.