Kaiser is the German word for "emperor" (female Kaiserin). In general, the German title in principle applies to rulers anywhere in the world above the rank of king (König). In English, the (untranslated) word Kaiser is mainly applied to the emperors of the unified German Empire (1871–1918) and the emperors of the Austrian Empire (1804–1918). During the First World War, anti-German sentiment was at its zenith; the term Kaiser—especially as applied to Wilhelm II, German Emperor—thus gained considerable negative connotations in English-speaking countries.

Especially in Central Europe, between northern Italy and southern Poland, between western Austria and western Ukraine and in Bavaria, Emperor Franz Joseph I is still associated with "Der Kaiser" (the emperor) today. As a result of his long reign from 1848 to 1916 and the associated Golden Age before the First World War, this title often has still a very high historical respect in this geographical area.