A vicar (ˈvɪkər; Latin: vicarius) is a representative, deputy or substitute; anyone acting "in the person of" or agent 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, such as an archduke, could be styled "vicar".
The Pope bears the title vicar of Christ (Latin: Vicarius Christi).
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.
Vicars have various titles based on what role they are performing. An apostolic vicar is a bishop or priest who heads a missionary particular Church that is not yet ready to be a full diocese – he stands as the local representative of the Pope, in the Pope's role as bishop of all unorganized territories. A vicar capitular, who exercises authority in the place of the diocesan chapter, is a temporary ordinary of a diocese during a sede vacante period.
Vicars exercise authority as the agents of the bishop of the diocese. Most vicars, however, have ordinary power, which means that their agency is not by virtue of a delegation but is established by law. Vicars general, episcopal vicars, and judicial vicars exercise vicarious ordinary power; they each exercise a portion of the power of the diocesan bishop (judicial for the judicial vicar, executive for the others) by virtue of their office and not by virtue of a mandate.