Birger Dahlerus was a Swedish businessman and personal friend of Hermann Goering. Shirer describes him as a "curious" fellow who played an equally curious role in the final negotiations and subterfuges between Germany and the West in the final months before the outbreak of the Second World War.
Shirer's opinion of Dahlerus isn't particularly high: he describes him as "well-meaning in his quest to save the peace," but "naïve and, as a diplomat, dreadfully amateurish" (3.15.23). As Dahlerus himself admitted years later, he allowed himself to be "badly misled by Goering and Hitler" (3.15.23).
Vidkun Quisling was a Norwegian politician, and if his name sounds vaguely familiar to you, it may because it gave us the term "quisling," which, as Shirer writes, is "a synonym in almost all languages for a traitor" (4.20.10).
Kind of like Benedict Arnold.
Like Arthur Seyss-Inquart in Austria, Quisling sold his country out to the Nazis as Hitler prepared to invade it. Later, he governed Norway as a collaborator during the Nazi occupation. Shirer writes that during his time as Prime Minister, "his unpopularity among the people was immense," but "his power was nil despite his best efforts to serve his German masters" (4.20.198).
After the war, Quisling was tried for treason and sentenced to death, and was executed in October 1945.