Carlo Ventresca (or Patrick McKenna) in the film is the Pope's Camerlengo and the surprise villain of Angels & Demons.
In the book, Robert Langdon and Vittoria Vetra are summoned to Vatican City by the Swiss Guard, who need them to locate the antimatter counting down within their walls and discover the secret behind the Illuminati ambigram. When Langdon requests entry to the Vatican Archives, he is led to the Camerlengo, who is currently the only person in the world allowed to grant them entry. As the four preferiti are murdered by the Hassassin, Janus, an Illuminati master, contacts the killer and gives him his orders.
As Langdon walks the Path of Illumination in an attempt to find the Illuminati lair, Carlo's history is slowly revealed as the story progresses. As a child, he never knew his father. His mother was a woman named Maria, whom he loved more than anybody else in the world. One day, she was tragically killed in an explosion, and Carlo was forced to work in the army. As he could not bear to kill another human being, he was given the job of a medical pilot. When he was still young, the Pope adopted him from the army and made him Camerlengo. However, shortly before his death, the Pope told him a secret which sickened Carlo and left him crying on his floor.
As the public were told that the Pope died from a stroke, the Hassassin contacts them and claims that the Illuminati were responsible for the death and poisoned him. When Vittoria confirms that he may have been overdosed on his own medicine and that the result would be very visible, she and Carlo visit the Pope in his sarcophagus and check his body; he has a completely black tongue, meaning he was poisoned as an effect of the overdose was the tongue turning black.