The Latin word Imperator was originally a title roughly equivalent to commander under the Roman Republic. Later it became a part of the titulature of the Roman Emperors as part of their cognomen. The English word emperor derives from imperator via Old French Empereur. 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 (derived from princeps, from which prince in English is derived) and the dominate.

In Latin, the feminine form of Imperator is Imperatrix, denoting a ruling female.

When Rome was ruled by kings, to be able to rule, the king had to be invested with the full regal authority and power. So, after the comitia curiata, held to elect the king, the king also had to be conferred the imperium.

In Roman Republican literature and epigraphy, an imperator was a magistrate with imperium (Rivero, 2006). But also, mainly in the later Roman Republic and during the late Republican civil wars, imperator was the honorifical title assumed by certain military commanders. After an especially great victory, an army's troops in the field would proclaim their commander imperator, an acclamation necessary for a general to apply to the Senate for a triumph. After being acclaimed imperator, the victorious general had a right to use the title after his name until the time of his triumph, where he would relinquish the title as well as his imperium.

Wolfgang Stark (born 20 November 1969 in Landshut), is a German football referee. He has refereed matches in the Champions League and qualifications to the European Football Championship and the World Cup. In 2007, he refereed five matches at the 2007 FIFA U-20 World Cup including the controversial semi-final between Chile and Argentina.

He was questioned for his performance overseeing the Chile–Argentina match in the 2007 FIFA U-20 World Cup, having "lost control of the match early" and for issuing seven yellow cards (out of nine) and two red cards against the Chilean team during the match. In total he issued 53 fouls, 30 of which he charged to Chile.

Following the match Stark and his colleagues were surrounded by livid Chilean players who were restrained by members of the Toronto Police. Stark then had to be escorted off of the pitch and into the dressing room tunnel by police officers for fear that he would be attacked by the crowd and/or Chilean players at the National Soccer Stadium. Chilean players, still angry after losing the match, fought with and were pepper-sprayed by police officers outside of the stadium. The players were temporarily held inside the stadium by the police for several hours and were released without being arrested.