Caesar, name of a patrician Roman family and an imperial title. The family of the Julian gens (clan) called Caesar was active in Roman public life from the time of the Punic Wars. The most renowned member of this family was Gaius Julius Caesar. His adopted son, Gaius Octavius, assumed the name Gaius Julius Caesar Octavianus in accordance with Roman custom, later adding the title Augustus (Latin, “majestic”), by which he is generally known. The four Roman emperors of the Julio-Claudian line—Tiberius, Caligula, Claudius I, and Nero—were also adopted into this family and thus properly called Caesar. After the dynasty ended with the death of Nero in AD 68, the name Caesar was retained to designate the imperial rulers. Emperor Hadrian adopted the imperial title Augustus; Caesar then became the title of the heir apparent to the Roman throne. In AD 285 Emperor Diocletian appointed a colleague, Maximian, to share the throne. Maximian was called Caesar until 286, when he was given the imperial title Augustus; two assistants, intended to be successors to the Augustuses, were selected and given the title Caesar. Each Augustus and each Caesar was assigned a portion of the Roman Empire to administer. Although this complex system did not survive, the title continued to be used for emperors-designate. The imperial significance of the title Caesar was preserved in medieval and modern derivations, including the German kaiser and the Russian czar.