An emperor (from the Latin "imperator") is a (male) monarch, usually the sovereign ruler of an empire or another type of imperial realm. Empress is the female equivalent. As a title, "empress" may indicate the wife of an emperor (empress consort) or a woman who rules in her own right (empress regnant). Emperors and Empresses are generally recognized to be above kings and queens in honour and rank.

Today the Emperor of Japan is the only remaining Emperor in the world.

Distinction from other monarchs

Both kings and emperors are monarchs. Within the European context, "emperor" and "empress" are considered the highest of monarchical titles, ironic in that "emperor" began as a military honorific in a staunchly anti-monarchical republic. Emperors were once given precedence over kings in international diplomatic relations; currently, precedence is decided by the length a head of state is continuously in office. Some emperors claimed inheritance (translatio imperii) of the political and religious authority of the Roman Emperors such as an important role in the state church; see Imperial cult and Caesaropapism. This inheritance has been claimed by, among others, the rulers of the Holy Roman Empire, the Byzantine Empire, and the Russian Empire; however, all types of monarchies have played religious roles; see divine right of kings and divine king. The title was a conscious attempt by monarchs to link themselves to the institutions and traditions of the Romans as part of state ideology. In contrast, many republics have named a legislative chamber after the Roman Senate.

Outside the European context, "emperor" is a translation given to holders of titles who are accorded the same precedence as European emperors in diplomatic terms. In reciprocity, these rulers may accredit equal titles in their native languages to their European peers. Due to centuries of international convention, this has become the dominant rule to identifying an emperor in the modern era.

Also, historians have liberally used "emperor" and "empire" anachronistically and out of its Roman and European context to describe any large state and its ruler in the past and present. "Empire" became identified with vast territorial holdings rather than the title of its ruler by the mid-18th century. Voltaire sardonically described the Holy Roman Empire as "neither Holy, nor Roman, nor an Empire" since by his time it was little more than an informal association of German states and its "Emperor", though at Voltaire's time ruler of Austria and king of Hungary and Bohemia, had almost no authority within the non-Austrian parts of the territory.

Roman tradition

In the Roman tradition a large variety in the meaning and importance of the imperial form of monarchy developed: in intention it was always the highest office, but it could as well fall down to a redundant title for nobility that had never been near to the "Empire" they were supposed to be reigning. Also the name of the position split in several branches of Western tradition, see below.