Batman (Batman: Assault on Arkham)

Batman is the masked vigilante who defends Gotham City.

Batman: Assault on Arkham
At some point, having discovered that the Joker had stolen a dirty bomb with enough explosive power to wipe out half of Gotham City, Batman tracked down one of Joker's accomplices in the plot, the Riddler, to his hideout in the Gotham docks in an attempt to track down the location of the Joker's dirty bomb. However, by the time he got to the hideout, it was raided by black ops soldiers from A.R.G.U.S., led by Amanda Waller, who were to take Riddler out for theft of data relating to the Suicide Squad. He then blacked out the hideout and, after neutralizing all of the soldiers, attempted to interrogate the Riddler on the location of the bomb. However, as the Riddler lacked any knowledge of the bomb's location, he then sent him to Arkham Asylum.

Later, he caught Harley Quinn raiding a toy shop for a Cutie Boo Boo doll, and after fighting her, he interrogated her regarding the location of the bomb under the assumption that she was still in league with the Joker, although she genuinely lacked any knowledge of the bomb either. After verifying that she was indeed being truthful, Batman then had her sent to Arkham Asylum. However, he was still suspicious about Harley Quinn wanting to get caught, and eventually discovered that a yellow-alert occurred at Arkham Asylum. He also deduced that the "live footage" was actually recorded footage being played of the Thursday shift, not the Friday shift, causing him to deduce there was indeed a situation at Arkham Asylum. He then encountered the Suicide Squad and fought with them in the storerooms, eventually dispatching Black Spider and disguising himself as the vigilante assassin. Eventually, he subjected himself to electroshock therapy while aiding the Joker while still in disguise, although the Suicide Squad eventually deduced he was Batman when they learned that "Batman's" head was blown off. However, before a confrontation could ensue, the surviving members of the Suicide Squad and Batman saw a message from the Joker (who had been freed by Harley Quinn earlier) revealing that he intends to give Gotham a lethal dose of "tainted love", and he is going to instigate a riot at Arkham Asylum in order to slow Batman down. Batman managed to deal with several escaped foes, including knocking out Zsasz by breaking a wall behind him, shoving Bane into the Gotham bay via the Batmobile, and stopping Poison Ivy when she placed the Arkham Staff under her control. Batman eventually tracked down Joker and Harley Quinn on a hijacked helicopter and fought off Harley Quinn while Deadshot fought the Joker. Batman, after defeating Harley Quinn, managed to disarm the dirty bomb, which had been in Harley Quinn's mallet.

Afterwards, Batman tried to warn the Suicide Squad handler, Waller, against such gambits in the future, although she ignored him.

Batman: Arkham Asylum
Two years later, Batman ended up having to stop a similar riot instigated by the Joker.

Trivia

 * Batman's defeat of Zsasz mirrored how he had dispatched of a goon in Batman Returns.