Some of Batman's most dangerous foes are sent to Arkham Asylum after being declared not mentally fit to stand trial. The inmates have been known to occasionally take over the Asylum and team up in order to defeat the Batman.
Most Notable Inmates
Possibly Batman's strongest foe, Bane has been incarcerated in both Blackgate Penitentiary and Arkham. During Bane's first attack against Batman, Bane made the Dark Knight face a gauntlet of his greatest foes from the Asylum.
Both criminals with the moniker of the Black Mask have been committed to Arkham, Roman Sionis and Jeremiah Arkham, the latter formerly being the director of the Asylum.
Most of the villains using the alias of Clayface have been inmates of the Asylum, including the most notable four - Basil Karlo, Matt Hagen, Preston Payne & Sondra Fuller
Harleen Quinzel was formerly a Psychiatrist at Arkham who was appointed to Joker which led to her corruption and transformation into the villain, Harley Quinn.
Hugo Strange is often depicted as an Arkham Asylum Staff member with him sometimes being director of the Asylum before he went into his criminal ways.
Arguably Arkham's longest residing resident, Joker usually takes the lead when orchestrating take overs of the Asylum. The Asylum was originally built purely to hold two inmates - Joker and Two-Face.
Killer Croc is one of Arkham's most dangerous inmates with him being kept under maximum security. Croc is also notable for biting the hand of Aaron Cash, a corrections officer in Arkham.
Mad Hatter is essential for the times when the inmates take over the Asylum as he utilises his mind-control technology to subdue the guards.
Man-Bat is an occasional ally of Batman, but is most often kept in Arkham.
Mr. Freeze is actually sane but is kept in Arkham Asylum as no other prisons hold the facilities needed to keep Freeze alive.
Penguin, like Mr. Freeze, has been shown to actually be sane and has spent time in Blackgate Penitentiary as well as Arkham. However, Penguin is usually committed to the Asylum anyway.
Possibly Arkham's most powerful inmate, Poison Ivy is usually kept under high-security.
Riddler is arguably Arkham's smartest inmate and has been shown to know all the possible ways to escape his cell.
One of the Asylum's deadliest residents, Scarecrow has been known to previously be a doctor at the Asylum.
One of Arkham's most tragic inmates, Arkham Asylum was originally built to only hold two-Face and Joker.