Azzolino was born at Fermo, the son of Pompeo Azzolino and Giulia Ruffo. He was the great-nephew of Cardinal Decio Azzolino, the elder and is thus often referred to as Cardinal Decio Azzolino, the younger.
As an agent of Donna Olimpia
These skills, among others, led to Azzolino becoming the principal Vatican decoder; responsible for cracking ciphers used in correspondence. He was also an able investigator. When the Kingdom of Naples was made aware of invasion plans (via the Kingdom of Spain), it was Azzolino who (in February 1654) concluded that the breach must have come from Camillo Astalli, the Pope's Cardinal-Nephew. Though likely accurate, his conclusion was convenient - Astalli was a rival for power to Azzolino's own patron, Olimpia Maidalchini. Contemporary John Bargrave noted that there were plenty of spies within the Vatican but that none excelled at the task more than Azzolino.
He participated in the papal conclave of 1655 which elected Pope Alexander VII. Azzolino was the leader of the independent liberal movement Squadrone Volante which played a role in engineering the result of the conclave in favour of an anti-nepotism candidate. Azzolino's Squadrone is also thought to have engineered the election of Giulio Rospigliosi as Pope Clement IX at the papal conclave of 1667. Rospigliosi, who had been Cardinal Secretary of State rewarded Azzolino by immediately (one the night of his election, in fact) appointing him to the position, giving further credence to the rumour.
Azzolino and Christina
Azzolino was appointed Queen Christina of Sweden's representative within the Catholic Church. After her death, Azzolino inherited many of her artworks, including Correggio's Danaë and Titian's Venus and Adonis. Some have speculated that he and Christina were in love with one another, though their relationship was never made public. It seems those in the Vatican, at least, knew of the relationship. Bargrave, again, suggested that Azzolino was sent to Romania by Pope Alexander in order to avoid public perception that a relationship was ongoing.
In a letter to Azzolino, Christina wrote in French that she would never offend God or give Azzolino reason to take offence, but this "does not prevent me from loving you until death, and since piety relieves you from being my lover, then I relieve you from being my servant, for I shall live and die as your slave". His replies were more reserved.
- Decio Azzolino by S. Miranda (Florida International University, last updated May 2012)
- Pope Alexander the Seventh and the College of Cardinals by John Bargrave, edited by James Craigie Robertson (reprint; 2009)
- History of the popes; their church and state (Volume III) by Leopold von Ranke (Wellesley College Library, reprint; 2009)