Ciano was the son-in-law of Benito Mussolini, and he served as Italy's Foreign Minister from 1936 until 1943, when he briefly became an ambassador to the Vatican. He helped to stage a minor rebellion against Mussolini.
Shirer draws heavily on Ciano's personal records throughout The Rise and Fall of the Third Reich, and the Foreign Minister's diaries give us some of the most striking character descriptions that appear in the book. For instance, here's his description of Hermann Goering in the winter of 1942:
We had dinner at the Excelsior Hotel, and during the dinner Goering talked of little else but the jewels he owned. In fact, he had some beautiful rings on his fingers... on the way to the station he wore a great sable coat, something between what automobile drivers wore in 1906 and what a high-grade prostitute wears to the opera. (4.26.32-33)
Shirer's descriptions of Ciano himself depict the Italian Foreign Minister as being much more suspicious of—and less easily swayed by—the Nazis than his fascist father-in-law. Ciano's diaries were often outlets for his frustrations concerning Nazi Germany's treatment of Italy.
After the Germans intervened in the rebellion against Mussolini, Ciano was executed by Il Duce under pressure from Hitler in January 1944.