Seems like ever since the mid-1980s, Batman has simply owned DC (maybe a certain amount of justice there, since the logo/name is a short for Detective Comics). However, that was not always the case. Time was, Superman was DC's clear leading brand (I can remember a cover of Superman touting him as the world's number 1 comics character).
Clearly, that changed. Anybody have an idea just when The Man of Tomorrow got dethroned?
note to mods: not putting this on the Supes forum because it involves Batman as well, and a more diverse array of opinion might be valuable.