Short answers, pulled from the story.
Galeazzo Ciano was an Italian diplomat and politician who served as Minister of Foreign Affairs of the Kingdom of Italy from 1936 to 1943 under Benito Mussolini, his father-in-law. He was widely regarded as Mussolini's most probable successor as head of government during that period.
Ciano was executed on the 11th of January 1944 after being convicted of treason at the Verona trial. He had voted in favour of the Grand Council resolution on the 24th of July 1943 that led to Mussolini's ousting. Mussolini, operating through his new Italian Social Republic government, ordered his death. He was shot by firing squad while tied to a chair, alongside four other men who had cast the same vote.
Ciano's diaries are a daily record he kept from shortly after his appointment as Foreign Minister in 1936 until his dismissal in 1943, covering meetings with Mussolini, Hitler, Ribbentrop, and foreign ambassadors. The diaries covering 1939 to 1943 were first published in English in London in 1946, edited by Malcolm Muggeridge. A complete English version was published in 2002.
Edda Mussolini attempted to barter Ciano's diaries to the Germans in exchange for his life. Her confidant Emilio Pucci, then a lieutenant in the Italian Air Force, helped recover some of the papers from Rome with Gestapo assistance. When Hitler vetoed the plan, Pucci helped Edda escape to Switzerland on the 9th of January 1944, two days before Ciano's execution, carrying five wartime diaries that she then buried beneath a rose garden.
Anthony Hopkins played Ciano in the 1985 four-hour HBO documentary-drama Mussolini and I. Frank Wolff portrayed him in The Verona Trial, a 1962 film directed by Carlo Lizzani.
Ciano's diaries were used by the prosecution at the Nuremberg Trials as evidence against Hitler's Foreign Minister, Joachim von Ribbentrop. Historian William Shirer also drew on them as a source for his 1960 book The Rise and Fall of the Third Reich.