Batman and the supporting characters share a similar background to those in the main continuity, parts of the characters origin and stories on Dark Knight Universe have been slurred or altered. According to Miller, the Batman that appears in All-Star Batman and Robin, the Boy Wonder is the same character who appears in Batman: Year One, The Dark Knight Returns, and The Dark Knight Strikes Again.
The Dark Knight Universe was created by Frank Miller.
Note:The Dark Knight Returns saga was assigned the number of Earth-31 after Infinite Crisis. But after Flashpoint such numeration was dropped at request of Frank Miller himself. It was changes to now The Dark Knight Universe.
Post-Flashpoint / The Dark Knight Universe
Unlike Batman on Earth-0 (the mainstream continuity), this Batman is much darker and significantly more brutal than his counterpart. He takes joy in causing his victims heavy amounts of pain, going as far as severely pummeling and burning his victims for his amusement. The story continues with Dark Knight III: The Master race.