Detective Arnold John Flass is a corrupted police officer that appears in the Batman comics. Even though he is a relatively minor villain, Flass plays a pivotal role in the origins of Batman. He is most often depicted as Jim Gordon's partner as well as a former Green Beret.
Flass first appears in 1987's Batman: Year One, in which he is characterized as a corrupt detective in the Gotham City Police Department and a former Green Beret. He is Jim Gordon's partner, and Gordon's first introduction to the ugly reality of Gotham City; on their first patrol together, Gordon witnesses Flass beating up a teenager for fun.
Flass, who has been in Mafia boss Carmine Falcone's pocket for several years, resents Gordon's strong moral character and worries that he will create problems for the department, which is built on corruption.
One night, Flass and several other officers accost Gordon and beat him mercilessly in order to "teach him a lesson". Gordon soon turns the tables on Flass, however, beating him up and leaving him gagged and bound in the middle of the woods.
Batman later intimidates a drug dealer named Skeevers, who turns on Flass and offers to testify against him. Then-Assistant District Attorney Harvey Dent offers Flass a plea bargain he cannot refuse: in exchange for testimony against Falcone and Police Commissioner Gillian B. Loeb, Flass would receive a lighter sentence. Flass accepts the deal and turns over extensive notes of his dealings with the Mob, giving Dent evidence to prosecute much of Gotham's organized crime.
After Year One, Flass made only occasional cameos in the Batman series. He is the third victim of the Hangman killer during the limited series Batman: Dark Victory which is set a few years after Year One; the Hangman seeks to eliminate everyone who helped Dent's career as D.A., regardless of their motives for doing so. By this time, Flass has become a bouncer at a sleazy strip club called the "Cheetah Room", where the Hangman killer lynches him.
Flass appears Christopher Nolan's live-action film Batman Begins as a supporting antagonist, portrayed by Mark Boone Junior. His appearance is drastically different from his comic book counterpart; in the comics, Flass is tall and muscular with a blonde flattop, whereas the Flass that appears in Batman Begins is short and overweight with long brown hair and a beard. Interestingly enough, this version of Flass has a striking resemblance to Max Eckhardt, a character in the 1989 Batman film directed by Tim Burton, who, like Flass, was also a corrupt cop in the employ of the city's most powerful gangster.
Like his comic counterpart, Flass serves as Jim Gordon's partner, but he also moonlights as a low-level enforcer for Carmine Falcone, which Gordon is aware of and greatly dislikes. Flass is a bully and a thug; his uncouth behavior knows no bounds; he even steals from a food vendor's tip box and laughs in the man's face (and when the vendor protests, saying he has kids to feed, Flass sarcastically says, "What, they don't like falafel?" referring to the fact that it was a falafel stand.)
Flass is present with Falcone and a group of his thugs at a drug shipment in Gotham's Narrows. He is among the first victims of Batman, and later on, is intercepted by Batman in an alley and interrogated about where some of the drugs were being shipped to (half was being sent to various dealers, and half were being sent to "the man in the Narrows," in Falcone's words; this person was later revealed to be Scarecrow.) He later appears at Arkham Asylum with other GCPD members when Batman battles Scarecrow to save Rachel Dawes.
He is last seen when he inhales Scarecrow's fear toxin when it is released by Ra's al Ghul, and hallucinates that two children running in the street are in fact monsters. He panics and tries to shoot the children, but Jim Gordon (who injected himself with Batman's antidote and is thus immune to the toxin's effects) knocks him unconscious and hand-cuffs him to a pipe.
After Batman Begins
According to The Gotham Times (a marketing site for The Dark Knight), Flass spends some time in a mental hospital after being exposed to the toxin, and Harvey Dent eventually indicts him on charges of corruption. After Flass is dismissed from the GCPD, he loses his disability pension. His fate after this is unknown.