Decades have elapsed since Alan Bullock wrote Parallel Lives, tracing connections and counterpoints in the lives of Hitler and Stalin.
Now Laurence Rees, former head of the BBC's TV History unit, has decided to use "millions of words of original eyewitness testimony" to have another go.
Some of Rees' points of similarity are banal. Hitler and Stalin "both came from outside the mainstream", each "dressed modestly", neither trusted any "intimate confidante", yet the two ended up as "the two most powerful warlords the world had ever seen".
More ambitiously and contentiously, Rees claims that "they both believed they had uncovered the secret of existence". Moreover, "both of them offered a vision of a future utopia".
Rees is a bit more interesting when he appraises differences in work methods.
He maintains that Hitler remained "always suspicious of any institutional attempt to restrict him" and was prepared to "dismantle any centralised structure that could potentially usurp him".
By contrast, Rees argues that Stalin's "own personality exactly matched what the new structures of the Soviet state required".
That thought is perhaps the wrong way around: the structures were moulded to suit a mistrustful, bureaucratic micro-manager.
Pitching one more book to add to the huge Hitler-Stalin library requires both finesse and panache.
Insisting on moral equivalence between the two tyrants would be a dead end.
Rees draws well on his sources, quoting them to impart a vividly unfiltered personal touch to events.
While that commentary may not change essential judgments about Hitler or Stalin, the asides are illuminating and often touching.
Nonetheless, a general reader may well already know the story of Barbarossa, the Nazi invasion of Russia, surely the most decisive military campaign in history.
As for a specialist, she can turn to Volker Ullrich or Ian Kershaw on Hitler, to Stephen Kotkin on Stalin, or back to Anthony Beevor for some battles.
My copy of Rees' book is littered with question marks, but that quibbling is a back-handed tribute to the cogent, pungent way in which Rees' opinions are expressed.
He suggests that Nazis might well have asked whether they possessed "the resources they needed in order to get the resources they wanted".
He indicts naked fear and "a blame culture that was all pervasive" for the failure to sack Stalin in 1941.
Throughout, the book is admirably combative.