"Leadership" is a surprisingly slippery term, especially in an entity like the Third Reich where Führerprinzip made for a chaotic administration in which informal networks determined political power. Ian Kershaw's two-volume biography of Hitler is one of the better starting points as Kershaw helped pioneer the notion of "working towards the Führer" in the Nazi dictatorship. Peter Longerich's biography of Himmler as well as Robert Gerwarth's biography of Himmler's lieutenant Heydrich (Hitler's Hangman). One of the best books on the elite produced in recent years is Michael Wildt's An Uncompromising Generation: The Nazi Leadership of the Reich Security Main Office which is an analysis of the SS's RSHA. Richard Overy's Interrogations: The Nazi Elite in Allied Hands, 1945 covers the surviving elite and their responses to the IMT while Norman Goda's Tales from Spandau: Nazi Criminals and the Cold War examines their divergent fates through the 1980s.