Jonathan "Johnny" Cartwright, also known as Mouse, is a member of the Wonderland gang who remained disfigured on the left side of his face after an accident involving fire but possess the innate ability to impersonate anyone by mimicking their voice and using skin grafts-made masks. Mouse is the close friend/brother-figure of Beth Kane and her second-in-command after Chuck Dodgson's arrest. He is also the son of the late Dr. August Cartwright and the grandson of the late Mabel Cartwright.
At some point in his life, Jonathan had an unspecified accident that left the left side of his face hideously disfigured, causing people, especially other children, to call him a "monster", isolating him and forcing him to stay always alone without any friends.
He had a mediocre relationship with his grandmother who wasn't pleased at his appearence after the incident and often treated him badly, resulting in him developing a certain level of fear for her.
In January 2003, while he and his father were out fishing, likely together with his grandmother, they found Beth Kane, washed up on shore after the car accident that killed her mother. They took her back to their home and when she woke up Beth was immediately terrified, only wanting to see her father again. August tried to calm her down and explained that he wanted Beth to become friends with his son. She constantly screamed at him to allow her to go home, but he only left to get her a sandwich. Then the girl asked Johnny why he covered his face only to learn that he is afraid of scaring people, and she explained that he didn't scare her.
Later, while Beth and Johnny were watching television, he showed her his ability to mimic any voice he hears perfectly, then a news report of the girls disappearance came on and she asked August why he hadn't called the police. However, he never answered but instead grabbed her and threw her into the basement and locked the door, later telling her that the only reason she was there was to become friends with his son.
Later, Beth managed to get to open the door, making her way to the kitchen and calling her father to ask for help, only to be cut off by August who grabbed the phone, ripping it off the cord, warning her that if anyone came for her, he would kill them and throwing her back into her cell right before instructing Johnny on mimic Beth's voice after Jacob and Kate Kane showed up at the house, demanding to know where Beth was. Though reluctantly, the boy executed his father's order and August managed to make Jacob believe that it was Johnny pulling a prank after having heard Beth voice in an video shown in television, prompting Jacob and Kate to eventually left.
Johnny then approached the door of Beth's cell, while she was crying, telling her he wanted to be her friend and sliding the book, Alice in Wonderland, underneath her door in order to keep her company.
Becoming MouseOver the following year, Beth and Johnny build a sibling-like relationship, to the point that the boy is said to be the most important person to Beth. In January 2004, on the occasion of Beth's birthday, Johnny visited her bringing her waffles and secretly a kitten she decided to call Chessy as in "Cheshire Cat". Later, the boy's father entered the room and Beth quickly hid the animal. The man said that his son told him about the occasion and light a candle on the waffles telling Beth to make a wish. After Beth did it, Johnny asked her what she wished for and the latter replied that she wanted to see her family again, to which August noted that saying the wish out loud means that it will never come true, then he exited the girl's cell together with Johnny.
Later, his father tried to make Johnny a mask of skin grafts, ending up enraged and unpleased at the results as it looks too unreal.Few days later, Beth tailored a sweater for Chessy and showed it to Johnny, however the boy's father suddenly entered the cell discovering about the kitten and ruthlessly killing him in front of the kids despite they begging him to simply let him free; then, noticing how well done was the sweater he forced the girl into helping him made skin masks after telling her that his father had already remarried and thus forgotten about her. Devastated, Beth complied to her kidnapper's request, eventually realizing Johnny's first realistic skin mask.
Later, the boy came into her cell thanking her for helping him "look normal" and bringing some fishing wire to fix the copy of Alice in Wonderland he gave her an year prior and that his father had destroyed in a fit of rage. Traumatized at the thought of being forgotten and abandoned, the girl look intensively at one of the book's illustration with the quote "It's no use going back to yesterday, because I was a different person, then"; this ultimately "broke" Beth, who radically changed the tone of her voice telling Johnny that from that moment on she would have called him her little "Mouse" and that he could call her "Alice" before inviting him to a "tea party".
His grandmother moving in
Sometime after that, due to her health having worsened to the point she became bounded to an oxigen tank, his grandmother moved in with him, his father and Alice, whose new personality had overwritten the previous to the point she didn't remember her former life. The day the woman arrived, August ordered his son to move all of his things from the attic and, after he asked almost scared how long would she have stayed the latter told him that she was now too ill to live by herself. The woman then entered and hugged the boy complimenting him for looking better and August for having "fixed" his face.
Around 2013, Beth killed his grandmother after she repeatedly abused her and, over the following year, she finally escaped from August under unknown circumstances, but remained deeply close to Jonathan, who had apparentely helped her rebel against his father causing an accident in which he was presumed dead.
Sent to Arkham
At some point, Jonathan was sent to Arkham Asylum for unknown reasons. During this time he was used as a guinea pig by his warden, Dr. M. Butler to perform some experiments with the Fear toxin. However he managed to escape during the outbreak caused by John Deegan.
Working with Beth
Two weeks after his escape, while Beth was held captive by her sister Kate and convinced to tell her what happened to her after she survived the accident, Mouse approached the two while they were stopping at Dusty's Roadside Diner during a trip on the road to the place that marked Beth's destiny and, posing as a waiter, he managed to drug Kate and take her to the Cartwright's old house.
After Jacob Kane and Sophie Moore found out that Kate was held at the shacks, they were confronted by Beth and Jonathan. While Beth took care of her father managing to stab him, Mouse attacked Sophie mimicking Kate's voice and nearly managing to subdue her before she was able to pry his mask off and knocked him loose as he stopped to put the skin graft on his face back on. As Kate arrived, she held a gun to Mouse's head, and entered the house right before Alice could kill Jacob, telling her to decide which is more important to her: killing Jacob or keeping Mouse alive. Alice figured that Kate was bluffing, but Sophie came in aiming her gun at her. Irritated, Alice said that killing Jacob would be too easy and if they all walk out, no one had to die. Kate released Mouse and he leaves with Alice.
Later, Mouse and Alice were reunited once more, and he surprised her with a copy of the same book he gave her many years prior, assuring her that he would escape her pool of tears. Alice said that he saved her, and gave him the face that she assembled from her stint as the Skin Pirate. Mouse said that he loved her, and Alice told her "dear brother" that she loved him too and she can help him became anyone he wanted to be. She vowed that once they're done with Jacob, he would never forget about her again.
Infiltrating Hamilton Dynamics
Sometime later, Alice and Mouse kidnapped Hamilton Dynamics employee Dean Deveraux in order for the first to made a mask of his face using skin grafts, and the second to wear it, mimicking his voice and infiltrating the society's lab posing as him to steal their newest secret project. After Mouse protested asking Alice why they were keeping the real Deveraux alive and she responded they had to keep a low profile due to being under her sister's radar, Mouse claimed Beth was changed and had gotten softer, prompting her to respond that he was the one who was changed, since he used to trust her, to which Mouse responded that he does and would have done whatever she asked him to do.
The following day, he infiltrated Hamilton Dynamics and entered the room in which the weapon was kept, being immediately intercepted by an equipe of scientist and Catherine Hamilton-Kane herself, who complimented "him" for having accomplished such a thing as making their weapon work properly. She asked him how does he resolved a specific engineering problem and, being unable to answer it, he saves himself saying it was classified information, to which Catherine reacted collegially pointing out that it could not be otherwise being it a weapon designed to penetrate Batwoman suit.
Shocked at the revelation, Mouse called Alice mimicking Kate's voice, thus extorting her the confession that Kate is Batwoman. Angered, he called Beth a traitor due to still wanting to protect her sister despite she abandoned her, and in a fit of rage killed Deveraux using the gun he stole from Hamilton Dynamics. ater that night Mouse went looking at Wayne Tower from the street and Alice joined him to comfort him, explaining she needed Kate for her "tea party" and that he wouldn't need to share her with Kate as they wold share Kate between one another. Heartened, Mouse asked what would happen if Kate "didn't want to play" to which Alice replied that in that case they already have the right weapon.
After the Rifle failed twice in killing Pyra Electrics' employee Derek Holcomb, the last man capable to replicate the weapon he previously stole, Mouse assaulted him on the street and brutally murdered him. Later, posing as Jacob Kane, he infiltrate Crows Security headquarter, where he was approached by Catherine Hamilton-Kane, who told him that the reason why Deveraux and Holcomb had been killed is that they were the only people capable to replicate the coil accelerator, Hamilton Dynamics' secret weapon that can penetrate Batwoman's suit.
"Jacob" agreed to let her know when his men would have found the weapon, and allowed her to oversee the operation after it was found in possession of the Rifle, who has a confrontation with Julia Pennyworth (disguised as Batwoman) after which the latter was captured by the Crows and subsequently freed by Kate. Catherine managed to convince "Jacob" to hold off filing for divorce stating that no matter how difficult everything went they could face it as long as they were together, however, after he returned to the Wonderland gang's hideout, getting rid of his disguise, it was revealed to be all part of Alice's machination to prepare her "Mad Tea Party".
Murder of Catherine Hamilton-Kane
Still disguised as Jacob Kane, while the real one was in Alice's captivity, Mouse accepted Mary Hamilton's request to join her and her mother at Gotham's annual Humanitarian Ball where Catherine would receive the Humanitarian Award. After discovering this, he was confronted by Kate, who asked him if he was getting back together with Catherine and how could he forgiven her for faking Beth's death, however "Jacob" claimed that he's not forgiving her rather starting to understand the reason because she did it; thus making Kate suspicious and prompting her to make him a trick question with a phone call discovering he was an impostor. Right after the girl managed to inform Sophie about her discovery with a message, Mouse drugged both her and her husband Tyler, later replacing all of the Crows agents assigned to the Humanitarian Ball security with Wonderland gang's members.
That night, he went to the Orpheum Theatre with Mary and Catherine, making a toast of champagne in the latter honor while on their limousine, thus poisoning both of them with a toxine developed by Hamilton Dynamics. Later, after Catherine was blackmailed by Alice through her teleprompter and forced to admit all of her crimes in front of the audience before collapsing due to the poison, he transported her to the back of the stage, then, while Mary called the hospital "Jacob" left stating that he was going to look for help.
Mouse then proceeded in keeping out of the building the GCPD while Alice completed her revenge forcing Catherine to sacrifice herself in order to save her daughter's life, giving Mary the only sample of the antidote; then, while an enraged Batwoman confronted Alice, Mouse intervened breaking the fight before fleeing with her.
During the Anti-Monitor Crisis, Jonathan as well as everyone in the multiverse except for the seven Paragons, was killed in an antimatter wave by the Anti-Monitor on December 10, 2019, only to be restored a month later, after the Paragons and the Spectre created a new universe.
Celebrating the victory
After killing Catherine, Alice and Mouse started visiting the cemetery daily, where they would have tea and spill the beverage on Catherine's grave as a "celebration" to mock her death. During one of said occasion, Mouse stated that Alice should abandon any hope for Kate to be part of "their family" once more since she would never forgive her or see her as anything else but broken as long as she was "playing hero".
Later, after Alice planted C-4 in Gotham Prep's hall and kidnapped Parker Torres in order to unmask Batwoman to the whole Gotham, Mouse detonate it by distance like he was ordered to do as a contingency in case said plan was thwarted, despite Batwoman, the Crows and GCPD managing to save everyone inside the building.
Kidnapping Gotham's golden boys
Mouse captured Steven Forbes, Commissioner Forbes son, and Bryan Akins, heir to Mayor Akins keeping them hostage and sending a video to the Crows to ask them to release Alice before 9PM in exchange to the boys safety. Later he and the Wonderland gang ambushed and caught also Kate Kane in order to prevent her from interfering his plans, thus bringing her in the scrapyard in which he kept the other hostages.He tried to use Kate to force Sophie into submitting to his requests, however Kate used a code they studied at the Academy to inform her former lover not to listen to him, buying enought time to Mary and Luke for preparing Beth's doppelgänger to pose as Alice, however after the latter asked him to free the hostages and failed a code they used since childhood, Mouse managed to see through the deception, threw her in the trunk of a car and set it on fire. However Kate managed to free herself and save the young men and Beth after defeating Mouse and his goons. Having been seriously injuried in the fight, after being arrested Mouse underwent surgery and is then placed in ICU at Gotham General Hospital with a six person team to monitor him.
Reunited with his father
There, he was visited by Alice, dressed as a Crows agent, right in the following day. At first he believed her to be the same impostor who tried to trick him the previous night, however, after she managed to complete a rhyme from Alice in Wonderland, she convinced him of her identity prompting Mouse to disclose to her about her doppelgänger. After noticing Alice's ear was bleeding, Mouse asked her what was wrong, to which she responded him that she needed to investigate and would have been back for him after she had found some answers, then she leaved the room.
Later that night he was visited by Dr. Ethan Campbell, who revealed to him to be his still alive father. The man stated that he would forgive his son for having betrayed him for Alice if he told him where she was so that he could kill her, to which Jonathan replied he would never do that as she was his real family due to August having raised him with the belief that he was a monster while Beth accepted and loved him. Hearing that, his father drugged him, sneaked him out of the Hospital and chained him inside a seemingly abandoned warehouse.
The next day his father visited him and revealed he killed Beth, also showing him a paper reporting the news of the villainess' death. As Mouse began to cry, he told him not to since all she did to him was using and manipolating him while he protected him from the world's cruelty. Angered, Mouse replied that the most cruel thing in his life was him, to which his father responded that soon he would have been able to see the truth, right before hooking him up to a canister of Fear Toxin.
Few hours later, after Alice rescued him, Mouse was in panic and repeated that she should be dead. However, the woman managed to answer correctly when he asked her their code word, causing him to be persuaded that his father simply killed a woman who looked like her. When Alice asked what was the place they were in, Mouse replied that it used to be his grandmother's house then explained that his father exposed him to the toxin in order to have him unveil his worst fear and that was revealed to be Alice herself, as she destroyed his family. Still under the effect of the toxin, Mouse bound Alice to a chair and hooked her up to the canister of fear toxin in his place, then he left the building.
Back to Arkham
Still under the toxin's effect, Mouse attacked a nurse out of Arkham and, the following day, went to the house of Tammy, one of the nurses who treated him while he was locked there. However he was arrested by the Crows and sent back to the asylum, where Dr. Butler locked him into isolation under the asylum's underground.
That night, Beth broke into the facility with Kate with the intention to free him. However, while she entered his cell and the two reconcile, her sister revealed that she was working together with Jacob all along to lock up both of them, and walked away after closing the cell's door leaving Beth inside it with Mouse.
That night, he listened eagerly at Alice, imprisoned on the floor above his cell, plotting her revenge and vowing to take his grandmother's place as the "Queen of Hearts".
Jonathan displays an obsession with Lewis Carroll's Alice in Wonderland, but is also quite well versed in pop culture; using his ability to mimic voices to cheer up Beth, by references films like The Goonies (1985), by quoting how, "Goonies never say die!"  and then he also uses his mimicry to sound like Emma Watson as Hermione Granger in the scene from the 2001 film Harry Potter and the Philosopher's Stone, when she tells Ron he's saying it wrong and that, "it's Leviosa, not Leviosar". He is also prone to jealousy to the point where he will kill an innocent person, because Alice is more focused on someone else. He has shown to be more connected to reality than Alice is, as unlike her, he knows for certain that Kate would never join their little family.
The only positive trait that Jonathan has is his undying love and loyalty towards Beth. He sees her as his one true family for she accepted him and loved him despite his horrendous appearance and was more than willing to protect her from his father's wrath.
- Voice mimicry: Mouse has the innate ability to mimic the voices of others exactly. He has used this talent to mimic various individuals, such as Beth and Kate Kane, Dean Deveraux, or Jacob Kane.
- Peak of human physical condition: Jonathan is shown to be in top physical condition. He was able to overpower Sophie and trap her in a chokehold. He was also durable enough that he could take a kick to the groin and keep going without slowing down.
- Master of deception/Manipulator: Jonathan is exceptionally talented in the art of deception, as he is able to fool and convince everyone while mimicking other individuals voices or posing as them.
- Expert hand-to-hand combatant: Mouse is proven to be a fearsome hand-to-hand combatant and martial artist, as he was able to match and nearly best a highly skilled Crows agent such as Sophie Moore in hand-to-hand combat.
- High tolerance for pain: Jonathan was impaled by a pipe during his fight with Kate in the scrapyard, but did not react in pain.
- Stealth: Mouse has great skills in stealth. He was able to sneak up on Sophie Moore and right behind Beth without them noticing him.
- Skin grafts: Mouse uses various skin grafts obtained from corpses to create fake faces in order to impersonate other people.
- Rail gun: Mouse used the specialized railgun that can penetrate Batwoman's suit.
- Knife: Mouse used this knife to kill Derek Holcomb.
Behind the scenes
- Johnny is the first case of gender-bending in since he's based on the villain Jane Cartwright aka Jane Doe, who first appeared in the Gotham episode "Nothing's Shocking". She was a serial killer and an Arkham Asylum patient, who was under the psychological delusion that her face was hideously disfigured and wore a mask at all times. She had the ability to shape-shift into other people by touching their skin.
- She was a composite character and based on two different Batman villains: Jane Doe, a master of disguise with the power of mimicry, and Calendar Girl; a supermodel deluded into thinking she was ugly that wore a similar mask.
- The comics version of Jane Doe is mentioned by Bruce Wayne of Earth-99 as an Arkham inmate.
- Johnny is also the third case of gender-bending in the Arrowverse where a female character was changed into a man. The first two were Lucious Coolidge and Heatstroke, making Johnny the first who isn't a fire-based villain.