Cardinal vicar

Cardinal Vicar (Italian: Cardinale Vicario) is a title commonly given to the vicar general of the Diocese of Rome for the portion of the diocese within Italy. The official title, as given in the Annuario Pontificio (under the heading "Vicariate of Rome"), is "Vicar General of His Holiness". The Bishop of Rome appoints the Cardinal Vicar with ordinary power to help with the spiritual administration of his diocese. Although canon law requires all Catholic dioceses to have one or more vicars general, the Cardinal Vicar functions more so than the others as a de facto diocesan bishop due to the Pope's many other responsibilities. There is a similar position dealing with the spiritual needs of the Vatican City called the Vicar General for the Vatican City State, or more exactly, Vicar General of His Holiness for Vatican City. He too is a cardinal.

It seems certain that in the twelfth century vicars were named only when the pope absented himself for a long time from Rome or its neighbourhood. When he returned, the vicar's duties ceased. This may have lasted to the pontificate of Pope Innocent IV (1243–54); on the other hand it is certain that in the latter half of the thirteenth century the vicar continued to exercise the duties of his office even during the presence of the pope at Rome. Thus the nomination of a vicar on 28 April 1299, is dated from the Lateran. The office owes its full development to the removal of the Roman Curia to Southern France and its final settlement at Avignon. Since then the list of vicars is continuous.

...
Wikipedia