Arkham Asylum is one of the most dangerous places to work, as the inmmates are constantly trying to get out, and will kill anyone to do so. Thus it's got a revolving door of security and doctors.
One such security guard that has fought through the pain is Aaron Cash. Brought into the world via an Arkham Asylum special, Cash is known for having his hand eaten off by Killer Croc. Despite this, he not only stayed, but he took some of Croc's skin and made a wallet.
In the comics, Cash still works at Arkham, and it was revealed that his son was actually killed by the Joker, though he didn't know it at the time. Cash appeared in the Arkham games as well, and every time he assisted Batman however he could.
Cash is a good soul despite everything that's happened to him. And he's always ready to take charge and help those who need it. Including Batman.