An antiking (German: Gegenkönig, Latin: contrarex, Czech: protikrál) is a would-be king who, due to succession disputes or simple political opposition, declares himself king in opposition to a reigning monarch. Antikings are more often found in elected monarchies than in hereditary monarchies like those of England and France; such figures in hereditary monarchies are more frequently referred to as pretenders or claimants.
Antikings are most commonly referred to in the politics of the Holy Roman Empire down to the beginning of the 15th century. The term is comparable to Antipope, a rival would-be Pope, and indeed the two phenomena are related; just as German kings and emperors sometimes raised up antipopes to politically weaken Popes with whom they were in conflict, so too Popes sometimes sponsored antikings as political rivals to emperors with whom they disagreed.
Several antikings succeeded in vindicating their claims to power, and were recognized as rightful kings: for example, the Emperors Conrad III, Frederick II, and Charles IV (see table below). The status of others as antikings is still disputed to this day: e.g., Henry II, Duke of Bavaria and Egbert II, Margrave of Meissen.