The word emperor can mean the male ruler of an empire. Empress, the female equivalent, may indicate an emperor's wife, mother/grandmother, or a woman who rules in her own right and name. Emperors are generally recognized to be of the highest monarchic honour and rank, surpassing kings. In Europe, the title of Emperor has been used since the Middle Ages, considered in those times equal or almost equal in dignity to that of Pope due to the latter's position as visible head of the Church and spiritual leader of the Catholic part of Western Europe. The emperor of Japan is the only currently reigning monarch whose title is translated into English as "Emperor".
Gaius Octavianus Caesar "Augustus", or simply Augustus, was the first emperor of the Roman Empire, reigning from 27 BC until his death in AD 14.
A statue of dictator Julius Caesar.
Under Justinian I, reigning in the 6th century, parts of Italy were for a few decades (re)conquered from the Ostrogoths: thus, this famous mosaic, featuring the Byzantine emperor in the center, can be admired at Ravenna.
Holy Roman Emperor Charles V in the 1550s, after Titian
The title of imperator originally meant the rough equivalent of commander under the Roman Republic. Later, it became a part of the titulature of the Roman Emperors as their praenomen. The Roman emperors themselves generally based their authority on multiple titles and positions, rather than preferring any single title. Nevertheless, imperator was used relatively consistently as an element of a Roman ruler's title throughout the Principate and the Dominate. The word itself derives from the stem of the verb imperare, meaning 'to order, to command'. The English word emperor derives from imperator via Old French: EmpereĆ¼r.
Carving in Diana Veteranorum referring to Lucius Verus as Imperator