If there's one thing Gotham City is never lacking, it's masked detectives, but Batman's home base experienced a twist on its usual vigilantes in Grant Morrison's Batman & Robin with the arrival of Oberon Sexton, known in his masked persona as the Gravedigger. An amateur detective and author, Sexton claimed to be on the trail of a globetrotting serial killer, leading to a team-up with the Batman Family.
At the time of Oberon Sexton's arrival in Gotham, Dick Grayson was actually the man under the Dark Knight's cowl following Bruce Wayne's apparent death in Final Crisis. ed by a petulant Damian Wayne as Robin, Grayson was still coming to grips with his new role, meaning Sexton provided vital . But little did the former Nightwing know that the surprise ally... was secretly Batman's greatest nemesis, The Joker.
Oberon Sexton first appears in Batman & Robin #5, being interviewed on Gotham This Morning. After being shown footage of Batman and Robin protecting the Penguin from the murderous Red Hood, Sexton defends the dynamic duo, pointing out that while they were defending a criminal, it was from a known murderer. Alfred later explains that Oberon Sexton is a famous writer from England, the author of Masks of Evil, who has taken up the name and costume of 'the Gravedigger.' Sexton even comes to Robin's aid when villains are sent to kill him, showing incredible combat skill with nothing but a shovel.
Thanks to his training as an international operative of the League of Assassins, this short interaction is enough for Damian to work out that Sexton's accent is fake. In a twist for both Damian and readers, the Boy Wonder plucks up the courage to ask if Oberon Sexton is a returned Bruce Wayne. It's a good guess, especially given that other of the Bat Family had found the Gravedigger "familiar," but Sexton denies the theory. It was a clever counter-reveal by Morrison, dashing one of the most prominent fan theories about Sexton's true identity, leaving only one real candidate for the face under the Gravedigger's mask.
Ultimately, it's Dick Grayson who figures out Sexton's identity, if not his true motives. Realizing that the victims of Sexton's serial killer quarry all died from 'joke' causes, Grayson accuses the Gravedigger of being the Joker in disguise... and the Clown Prince of Crime quickly unmasks to reveal the new Dark Knight is as skilled a detective as his predecessor.
While Oberon Sexton was a real person, Joker killed him and took his identity prior to his first appearance (Joker reveals Sexton killed his wife in a brilliantly planned plot, leading Joker to bury him alive with her body). Most interestingly, Joker claims his new role was genuine; with Bruce Wayne dead, the Joker has decided to try his hand at solving crimes - an early version of the core idea that would spawn Batman: White Knight stories.
Sadly, Joker's turn to the 'good' side is short lived. After defeating Doctor Hurt - the major antagonist of Morrison's run - Joker laments that he was wrong to think he had found a worthy opponent, and Bruce Wayne's return sees him immediately resume his role as Batman's nemesis. As a ghoulish finale, Joker buries Doctor Hurt alive, revealing that his adoption of the Gravedigger persona wasn't chosen randomly, but rather as a direct threat to his opponent he was always planning to carry out. You can't say The Joker is a one-note villain.
