A vicar (/ˈvɪkər/; Latin: vicarius) is a representative, deputy or substitute; anyone acting "in the person of" or for a superior (compare "vicarious" in the sense of "at second hand"). Linguistically, vicar is cognate with the English prefix "vice", similarly meaning "deputy". The title appears in a number of Christian ecclesiastical contexts, but also as an administrative title, or title modifier, in the Roman Empire. In addition, in the Holy Roman Empire a local representative of the emperor, perhaps an archduke, might be styled "vicar".
The Pope uses the title Vicarius Christi, meaning the vicar of Christ. The papacy first used this title in the 8th century; earlier they used the title "vicar of Saint Peter" or vicarius principis apostolorum, the "vicar of the chief of the apostles".
In Catholic canon law, a vicar is the representative of any ecclesiastic entity. The Romans had used the term to describe officials subordinate to the praetorian prefects. In the early Christian churches, bishops likewise had their vicars, such as the archdeacons and archpriests, and also the rural priest, the curate who had the cure or care of all the souls outside the episcopal cities. The position of the Roman Catholic vicar as it evolved is sketched in the Catholic Encyclopedia, 1908.