Autokratōr (Greek: αὐτοκράτωρ, plural: αὐτοκράτορες, Ancient Greek pronunciation [autokrátɔːr], Byzantine pronunciation [aftoˈkrator] lit. "self-ruler", "one who rules by himself", from αὐτός and κράτος) is a Greek epithet applied to an individual who exercises absolute power, unrestrained by superiors. In a historical context, it has been applied to military commanders-in-chief, and to Roman and Byzantine emperors as the translation of the Latin title imperator. Its connection with Byzantine-style absolutism gave rise to the modern terms and . In modern Greek, it means "emperor", and the female form of the title is autokrateira (αὐτοκράτειρα, "empress").
The title appeared in Classical Greece in the late 5th century BC, and was used for generals given independent authority, i.e. a supreme commander (stratēgos autokratōr). In Classical Athens, stratēgoi autokratores were generals endowed with autonomous power of command, i.e. they were able to make certain military and diplomatic decisions without prior consultation with the Athenian assembly. This was enacted when the general was expected to operate far from Athens, for instance during the Sicilian Expedition. Nevertheless, the generals remained accountable to the assembly for their conduct upon their return. Similar practices were followed by other Greek states, such as Syracuse, where the post served as a power base for several of the city's tyrants. Stratēgoi autokratores were also appointed by various leagues of city-states to head their combined armies. Thus Philip II of Macedon was declared as hēgemōn and stratēgos autokratōr of the southern Greek states by the League of Corinth, a position later given to his son Alexander the Great as well. The term was also employed for envoys entrusted with plenipotentiary powers (presbeis autokratores).