- "It's amazing what people believe...just because it's on the Internet."
- Good Scars, Evil Scars: Evil
- Laughably Evil
- Manipulative Bastard
- Monster Clown
- No Sense of Direction: has an habit of breaking and entering in the wrong places.
- Oral Fixation: Likes to smack his lips a lot.
- Roaring Rampage of Revenge: While he was locked up in Arkham between Seasons 1 and 2, a group of guards liked to beat the crap out of him on a regular basis (not that he didn't deserve it). In Season 2 he's spending his time hunting them down and murdering them one by one.
- Serial Killer
- Stalker with a Crush
- Suddenly Shouting: "I guess I'm gonna have to just KILL THEM!"
- The Only One Allowed to Defeat You: "You do NOT get to do that!"
- Villain Protagonist
- You Are Number Six: Is referred to only as Patient 4479. He refuses to or is unable to supply his real name, and the majority of characters would rather call him 4479 than Joker.
Dr. Harleen Kopski née Quinzel
- Brainy Brunette: She's a psychologist and surprisingly not blonde yet.
- Break the Cutie: A trip through the Valley of Fear finished the job Mr. J started.
- The Faceless: It's a while before we see her on camera.
- Meaningful Name: The Joker points it out — she's heard it before.
- Missing Mom: Harleen's mother abandoned her family for another man, which did a psychological number on her.
- The Shrink
- Tranquil Fury: Her demeanor after recovering from Scarecrow's fear gas.
- "Well Done Daughter" Gal: One of the root causes for Harleen's eventual Sanity Slippage is her obsessive need to prove to her father that she is not like her mother, who ran out with another man.
- You Look Familiar: Is played by the same actress who played Arkham's wife in season one.
Dr. Jeremiah Arkham
- Anti-Villain: His main motive above all else is to save his comatose wife.
- Big Bad: Shaping up to be this for Series Two.
- Beard of Sorrow: Appears to be growing one of these.
- Composite Character: The storyline involving his wife is similar to that of Mr. Freeze and Nora.
- Deadpan Snarker: Even in the face of death and danger, he's perfectly willing to match wits with Joker.
- Distressed Dude
- Face-Heel Turn
- From Nobody to Nightmare
- He Who Fights Monsters: In Season 2, to the point of recruiting Scarecrow to work for him by promising his old job and office back in return.
- Trauma Conga Line: First, Arkham is carjacked by the Joker and forced to act as an accomplice to his kidnapping of Bolton. Then he is taken to his house, tied up along with his wife, and told that a bomb will kill her at midnight unless he follows his instructions. Then, after the church incident, he escapes in the middle of shootout between the Joker and Gotham police, only to be captured again after the Joker commandeers a squad car. Then, after being forced to sell the asylum to Lex Luthor, he watches as his house blows up with his wife still inside it. She survives, but is in a vegetative state with little chance of recovery. That in a nutshell is what amounts to his Start of Darkness.
- Woobie, Destroyer of Worlds: His repeated traumas and humiliations at the hands of the Joker (sometimes played for Black Comedy) leads to him becoming one of the main villains of Season 2.
- Distressed Damsel
- Morality Chain: Further Evidence #2 reveals that for many years she was the only thing keeping Dr. Arkham from being evil.
Dr. Jonathan Crane
- Chekhov's Gunman: In his brief cameo early in Season 1, he provides a very literal example of how the villainous masks of Gotham's criminals interfere with their ability to live a normal life, and threatens Dr. Quinzel, who was given his old office. In Season 2, Dr. Arkham recruits him by promising him his office back.
- I Call It "Vera": His latest fear toxin formula, "The Valley of Fear".
- Malevolent Masked Men
- Oh, Crap: His face after seeing Harleen recover from his fear gas.
- Saved by Canon: It's a given Crane will survive the night since he has a cameo in The Dark Knight Rises.
- Bald of Evil: Although not as evil as usual.
- Boom, Headshot
- Pragmatic Villainy: Ultimately considers acquiring Arkham Asylum more trouble than it's worth, and agrees to sign it back over to Dr. Arkham. However, Arkham thinks this is merely Lex Luthor Code for "As soon as I get out of here I'm paying a hitman to shoot you in the face", so he has Two-Face shoot Lex in the face instead.
- You Look Familiar: Same actor as Hugo Strange.
Dr. Hugo Strange
- What the Hell Is That Accent?: According to the actor, it started off a Germanic accent, then it mutated into some sort of Jamaican accent while filming.
- Start of Darkness: Dr. Strange has left Arkham and plans to start his own clinic, with a special interest in the psychology of the Batman...
- Batter Up
- Butt Monkey
- The Brute: Becomes this after the Joker's rampage.
- Dumb Muscle
- Orderlies Are Creeps
- Sanity Slippage
Ted the Bum
- Better Living Through Evil: He says he's cooperating with the Joker because he wants to die, but you can tell the respect is a factor.
- Canon Foreigner: Appears to be a completely original character rather than an existing Batman or DCU personality.
- Death Seeker
- Multiple-Choice Past: His claiming to have held wildly varying jobs is a Running Gag. But it appears he was telling the truth when he claimed to be a fired GCN cameraman (who was married to Summer).
- Punny Name: His full name is apparently Theodore Bayer. Say it out loud.
- Of course he does work for the Joker. It could be an alias with the pun being intentional.
- Wild Hair: In Season 2 he has long hair and an unkempt beard, making him look much more bum-like than in Season 1.
- Why Do You Keep Changing Jobs?: "I used to be a..."
Dr. Thomas Elliot
- Anything That Moves / Bi the Way: Beds every guy he puts his eyes on. And Selina Kyle.
- The Casanova: Is apparently able to charm men into bed in extremely short order, usually starting with just a smile. Although, since they are men, this may have more to do with certain other tropes than it does with this one.
- Mythology Gag: "I like to keep my involvement with the Wayne family Hush, Hush.
- He also threatens to rip Selena's heart out.
- Saved by Canon: Selina was a major part of The Dark Knight Rises. She'll be fine.
- Even The Gay Men Wants Her: Is first introduced by seducing the until then extremely gay Thomas Elliot.