Henry Adams

"Oh Bats, you're so easy! Desperate to see the good in people especially when they're bad."

- Henry to Batman while revealing himself to be infected.

Highly respected principal of the esteemed McCallum Academy, Henry Adams was exposed to Joker's blood during a routine treatment at Gotham General. Displaying none of the symptoms experienced by the other victims, Henry's infection acts like an immunity that could be the key to developing a cure. Though initially cooperative, Henry's patience is wearing thin, and he's desperate to return home to his family.

Before Arkham Knight Incident
Henry Adams was the former Headmaster of the McCallum Academy, one of Gotham City's most prestigious schools. Because Henry had a hip replacement, he needed a blood transfusion.

When Joker sent samples of his mutated blood to hospitals all over the state, Henry and four other people were infected with his blood. Because Henry's blood and the other transfusions went unrecorded due to hospital errors, he didn't receive the cure. All of those infected except for Henry began to look and act like Joker, though Henry appeared to be immune to Joker's blood. If anything, Henry's personality actually improved following the transfusion. Batman (who was also infected) brought all four of the infected people to a containment facility and had Robin run tests to investigate why Henry wasn't like the others. At some point prior to this, he also paid a visit to Harley Quinn, the Joker's former lieutenant, and ended up displaying similar elements to the deceased Clown Prince of Crime, including a knack for telling extremely dark jokes.

Henry also had a wife. Batman informed the wife of the necessity of taking Henry into captivity and made sure to provide her with her needs during Henry's stay at Panessa Studios.

Arkham Knight Incident
Henry Adams was reported missing, with at least one missing flier posted at Pauli's Diner. At some point, Commissioner Gordon came to the quarantine and encountered Henry as well as the other Joker-infected people, with Batman explaining who they were.

Henry then made a plan with Quinn to get her and her gang in to liberate himself and the other Joker-infected victims to be adopted by her, went by the call-sign of "Mr. J", and also specified that Quinn needed to whack him on the head to ensure that Batman thought that Henry was on his side. Harley Quinn and her henchmen took over the facility and gathered the Joker clones so that her love's legacy would live on through them. Batman and Robin defeated the Joker clones and captured Harley, but the hostages were killed by Henry who was revealed to have succumbed to Joker's blood and wanted only the best of the infected to be the new Joker. When he confronted Batman, Henry realized that he was also infected and would be an even better Joker and shot himself in the head to "purify the gene pool".

Personality
At first glance Henry appeared to be a helpful and cooperative man who did everything he could to assist Batman and Robin in finding a cure for the Joker infected. He has also shown to be technologically intelligent and a respected Headmaster of the McCallum Academy. Batman's patient log for Henry Adams mentioned that the Joker's transfusion actually improved his overall personality, implying that Henry may have been something of a grouch beforehand.

After revealing himself to have to succumbed to the Joker Infection, Henry's true personality post-infection is revealed to be a ruthless, devious, manipulative madman. Henry is clearly insane and sadistic, mocking Batman for his beliefs that there was good in people and ranting about evolution just after executing defenseless prisoners. Henry has also taken up the Jokers egotistical nature, describing himself as the "strongest" before shooting himself in the head upon realizing that it was in fact Batman who was the "strongest". He also may have inherited Joker's suicidal nature, as he decided to commit suicide upon learning Batman would make a better "Joker" than himself. As evidenced by his first audio log, he had a tendency to tell extremely dark jokes, although it's implied that this was the result of Joker's blood taking hold of him.

Like the other other infected, Henry had taken on several personality traits of The Joker that influenced his way of thinking, in this case since he was a former biology teacher his reasoning was along the lines of evolution viewing himself as the strongest evolutionary patient compared to the others. Whether it was having been exposed the longest or that the infection adapted in a different way, Henry did not act out in the way that the other infected did as evidenced by each of them inheriting a specific personality trait (Johnny Charisma demonstrating the showman side of Joker, Christina Bell showing the obsessive love/hate side of Joker, and Albert King showing his arrogant/violent side) instead planning and biding his time so that he could gain control and kill the other infected whom he saw as inferior.

Henry was willing to wait long periods of time in order to properly observe and sabotage the facility Batman was using to treat the infected and showed other traits of the Joker including his ruthlessness and disdain for others who he saw as lesser than him including the infected and Harley Quinn when he used her for a human shield/hostage against Batman despite working together with her.

Arkham Knight

 * "It's Mr. Adams. We spoke on the phone." (Harley Quinn)
 * "Thank you for agreeing to see me, Ms. Quinzel." (Harley Quinn)
 * "Well, it's not everyday I have a gun pointed at my face. It's rather exciting, isn't it?" (Harley Quinn)
 * "Oh, I'm just remembering an old joker-sorry, I mean joke." (Harley Quinn)
 * "What's red and flat?" (Harley Quinn)
 * "A baby under an anvil." (Harley Quinn)
 * "Why couldn't the policeman catch the thief?" (Harley Quinn)
 * "Because his legs had been cut off!" (Harley Quinn)
 * "A father takes his family to the amusement park." (Harley Quinn)
 * "They all die in a car crash on the way home!" (Harley Quinn)
 * "Oh, poor Harley. I've missed you too." (Harley Quinn)
 * "Henry. Henry Adams. What is this place Batman? Where am I?"
 * "Sick? I've never felt better in my whole life." (Batman)
 * "Absolutely not. Those people, in the other cells, who are they?" (Joker Infected)
 * "WHAT? I mean, I'm not the only one?" (Batman)
 * "Those smiles. I've seen that before. It's him. The Joker." (Joker Infected)
 * "We're in danger Batman. You can't risk that kind of evil escaping into the world. You should kill them, all of them. It's the only way to be sure."
 * "Mrs. Q. This is Mr. J. Come in. Over." (Harley Quinn)
 * "My infiltration remains utterly flawless. Operation Puddin' Break is a go." (Harley Quinn)
 * "They're in rude health my dear. All dying to meet Mommy. Now, you remember the plan, don't you?" (Harley Quinn)
 * "We've been over this, my little knuckle duster! It's the only way to convince Batman that I'm to be trusted. You do want to kill him, don't you?" (Harley Quinn)
 * "Ooh, rat tat tat! Bird Boy's coming! See you soon. Mr. J, over and out." (Harley Quinn)
 * "Commissioner! Thank God. You have to get me out of here. They've locked me up, running tests like I'm some kind of guinea pig. There's nothing wrong with me!" (Commissioner Gordon)
 * "I've co-operated. I've done everything you asked. You said it would only take a few days!" (Batman)
 * "Batman. I hope you can hear this. The movie studios are under attack. Robin is in trouble."
 * "Of course. Tell me what-"
 * "I'm not a threat." (Harley's Henchmen)
 * "I don't know. I think something hit me on the back of the head." 
 * "They were crazy. You need to find them. Help them."
 * "Of course. I take it this means you stopped one of those monsters." 
 * "Of course. Anything."
 * "OK. I'll try. Computers really aren't my speciality."
 * "Like this? Oh, this technology is very......interesting. OK. I can see the camera."
 * "Done."
 * "Batman, please, you have to help me. That Quinn woman and her goons are trying to break in here! There's no telling what she'll do to me!" (Harley Quinn)
 * "Oh, Bats. You're so easy. Desperate to see the good in people." 
 * "...Especially when they're bad."
 * "Honey, I'm home!"
 * "Oh ho, I guess we now know who reprogrammed your security."
 * "Now, if you would be so kind... Go join your friend over there." (Batman)
 * "Now." (Gun to Harley's stomach)
 * "Evolution's a funny thing..." 
 * "No matter how many obstacles get in its way, the strongest always survives." 
 * "Still, you know what they say about evolution? Even amoebas can do it."
 * "Purifying the gene pool." (Harley Quinn)
 * "Goodbye. It's been... educational." (Gun pointed at Batman)
 * "Now that's... Unexpected. You're going to be… spectacular." (Batman)

Trivia

 * A close look at Henry Adams' face showed that he looked like an elderly version of the Joker, which foreshadowed that he wasn't actually immune to Joker's blood.
 * That elderly look could also be a reference to the Elseworld story Kingdom Come, where an elderly Joker mildly resembled Henry Adams.
 * Who Henry shoots depended on which of the Jokerized victims was rescued last.
 * Henry Adams' codeword for causing the breakout after reprogramming the Bat Computer at the movie studios: "Honey, I'm home!" was the same codeword Joker himself used to instigate the Arkham Asylum jailbreak/riot in Batman: Arkham Asylum.
 * The aspect of Joker's personality that Henry took on the most was Joker's intelligence and deceitfulness, as shown when he was able to trick both Batman and Robin into believing that he wasn't infected. Henry may also have symbolized Batman's futile, far-flung hope that the Joker had an ounce of good left in him that could have lead to redemption.
 * Henry has several missing posters in Gotham. One poster is found in the intro on the Fridge in the diner.
 * Despite standing at 5'9" (175 cm), Henry's missing poster said that he was 64.80 inches which is 5'4".
 * Henry is voiced by Garrick Hagon, who co-starred as Biggs Darklighter with Mark Hamill (the Joker's voice actor) in the original Star Wars film.