Archbishop Gilday is a fictional character and one of the main antagonists in The Godfather Part III. He is portrayed by Donal Donnelly. His character is said to have been based on Paul Marcinkus.
Gilday is an Irish American archbishop in the Roman Catholic Church, and also the head of the Vatican Bank. At the outset of the film, he bestows one of the Church's highest honors, the Order of St. Sebastian, on Michael Corleone. Later, at a meeting with Michael and B.J. Harrison, he convinces Michael to deposit $600 million in the Vatican Bank in exchange for majority control over International Immobiliare, a European real estate company in which the Church owns a quarter interest. However, it is all a scam: Gilday, along with the Bank's chief accountant Frederick Keinszig and Don Licio Lucchesi, had conspired to swindle Michael out of the money and give it to pezzi da novanta (bigshots) in high political places. He even backs Michael when his ownership of Immobiliare is threatened by other shareholders, in order to give Michael the impression that he is his ally, but constantly brings up the ill health of Pope Paul VI (whose approval was needed to ratify the deal) in order to stall the deal and highlight his own supposed powerlessness in the situation.
However, when his scam is about to be exposed by Cardinal Lamberto (the new Pope John Paul I), Gilday conspires with Lucchesi and Keinszig to poison the Pontiff's tea. After Vincent Mancini-Corleone succeeds Michael as head of the Corleone family, he orders the deaths of Gilday, Keinszig, and Lucchesi as revenge for swindling Michael. Accordingly, Michael's personal assassin Al Neri steals into the Vatican at night and shoots Gilday as the latter climbs a set of circular stairs. Neri then throws the Archbishop's corpse down the gap between the circular stairs.