An autocracy is a system of governance whereby absolute power is held by a single person. Autocracies are similar to totalitarian regimes and dictatorships, but differ in several ways.
Autocracy is a government system which relies on a single person possessing unlimited power. The sole leader is referred to as an autocrat, which is derived from the ancient Greece model in which the "autokrator" was referred to as the "self-ruler" or "one who rules by himself."
Modern day autocrats are associated with despots, dictators and tyrants, although they each have their own separate and distinct meaning. Autocracy and totalitarianism are also orthogonal concepts; autocracy represents unlimited power, while totalitarianism looks to regulate every aspect of private and public life. In addition, an autocracy always has a single ruler, while a totalitarian government is not necessarily based on singular rule.
Historically, defining an autocracy has proved difficult because most autocrats require some kind of power structure to rule. Famous examples of autocratic societies include the Byzantine Empire, Soviet Union and Nazi Germany. Russian emperors even included "autocrat" in their official title. The origin of this use dates back to the Byzantine Empire where "autokrator" was employed with "basileus" to denote emperor. Modern Greek still uses this term when referring to any emperor, regardless of actual power over state.