A very old Immortal, and a high-ranking member of the Roman Catholic Church, he was a Vatican bureaucrat.
According to the screenplay of Highlander: The Source, Giovanni was born in the year 30 BC, location unknown, possibly somewhere in the Roman Empire.
Giovanni was alive during the time of Jesus of Nazareth. In later centuries, after reviving as an Immortal, he began to experience guilt over not playing some role in preventing the Crucifixion, this guilt fueled his decision to embrace the teachings of the Roman Catholic Church.
Around this same time, Giovanni became Immortal; circumstances and location unknown. After becoming Immortal, Giovanni gloried in his new life, amassing a fortune and wallowing in excess. But as he rose in power and stature, his own resurrection started to weigh heavily on his mind, and he began to believe that God has chosen him to be His “messenger.”
According to the film's script, Giovanni was present at the fall of Rome to the Visigoths under Darius and Grayson, and The Kurgan. The destruction of the city would greatly pain him for centuries to come. In the year 1249, Giovanni served as a Knight Templar during the Seventh Crusade.
In the year 1860, Duncan MacLeod and Giovanni crossed swords in Rome, when MacLeod sought to help usurp King Victor Immanuel’s ruler-ship of Italy. Both were arrested in the middle of the duel by Garibaldi’s “Red Shirt” soldiers and briefly imprisoned, though Duncan didn’t hold a grudge against Giovanni for the incident in later centuries.
He proved himself to be a feckless, whining, self-centered, and self-involved creature. Giovanni embarked on a quest to search for The Source, the origins of all Immortality, alongside Duncan MacLeod, Methos, Zai Jie, and Reggie Weller.
Ultimately, however, awash in his own arrogance, Giovanni abandoned his comrades, and tried to go to The Source alone, where he met his end at the hands of The Guardian.
He was summed up aptly by Methos: "You know, Giovanni, I saw Christ teach, I saw Christ heal -- you, you self-centered son of a bitch, are no Christian!"