The Dark Knight Returns was recommended to me by a friend who suggested that without it, there would be no cinema Batman as portrayed by Michael Keaton and Christian Bale (let's leave Val Kilmer and George Clooney aside!)
In it, Batman is ageing and bitter, and has suppressed the Dark Knight to live full time as Bruce Wayne. But looking around an increasingly liberal and permissive world, he finds that he cannot stand by and do nothing.
Batman is portrayed as the real man, for whom Wayne is a mask, and he is an unapologetic right-wing militant. Whilst I disagree with Miller's portrayal of a liberal world as an inherently wrong one, it is an exemplary study of what drives Bruce Wayne.