- "Hello, brother. Didn't think you could get rid of me so easily, did you? See, my days were numbered but you, oh, you'll continue on for me. Be my ultimate revenge! So, calm yourself. Don't fight it. Breathe it in. This gas was a special mixture I made, just for you. Something to finally set you free. It's time to have some fun. Burn it down, brother. Burn it all down!"
- —Jerome Valeska in a recording for Jeremiah[src]
Xander Wilde (born Jeremiah Valeska) is the identical twin brother of the anarchistic criminal Jerome Valeska. Jeremiah, an intelligent and wise individual, suffered years of abuse at the hands of his psychopathic brother, which even burnt Jeremiah's bed while Jeremiah himself was in it alive.
In a desperate attempt to defend Jeremiah from his monstrous brother, his uncle took him away from Haly's Circus, in which his mother Lila works, and took him to St. Ignatius. Right after that action, he has changed his name and started calling himself Xander Wilde. After finishing school, Jeremiah or rather Xander Wilde has become a high-level intelligent engineer, and since a young age, he used to deal with labyrinths and built a hideout of his own to protect himself from his brother, which took almost six years of construction. In addition to the hideout which he filled with security cameras, rooms of work and more, he met a young woman named Ecco which started to work for him as a proxy and assistant. Jeremiah would later reunite with his brother, which after a rampage to find his twin, found him in his hideout.
Right after witnessing his brother's death, it was revealed that he was still a pawn in Jerome's secretive master plan; transform his brother into what he was, an lunatic maniac, and he indeed succeeded by doing so when Jeremiah opened the gift which was sent to him by his brother, and eventually inhaled the "special" gas created by Jerome, and went drastically insane, his face becoming pale white and a wide red grin forming ear to ear.
Xander was born (Jeremiah Valeska) to Lila Valeska and Paul Cicero. Jeremiah also had a twin brother named Jerome, who would (supposedly) abuse and scare Jeremiah when he was little, at least according to Jeremiah. Jeremiah (supposedly) realized Jerome was dangerous and knew he needed to get away from him so he snuck away one night from Haly's Circus and had his uncle place him at St. Ignatius. Shortly afterward Jeremiah changed his name to "Xander Wilde". He would then study at school and become an engineer.
Four years after graduating, he started construction on his hideout out of town. The building took 6 years to complete.
At an unknown point in time, he met a woman named Ecco and he hired her as his proxy and assistant.
Reunited With Jerome
Ten years after Xander's graduation, Jerome breaks out of Arkham Asylum and Kills their uncle, Zachary at the diner he owns for the location of Xander.
Xander is then confronted by the stunned Captain Jim Gordon and Detective Harvey Bullock. They ask Xander about him and Jerome, he tells them that once Jerome tried to kill him, so he ran away and changed his name to Xander (his birth name is Jeremiah Valeska). They then find out that he‘s holding Jerome captive, so they immediately order Xander to let him go but he refuses to do so. After finding out that the Legion of Horribles is inside the building, and that they hypnotized Ecco, Xander takes Jim and Harvey into the halls of his house, which were built as a maze that he’s the only one he can get out of. The three find Ecco there but, since she was hypnotized by Tetch, she gets into a fight with them, Ecco easily wins and takes Xander to Jerome, but she’s eventually knocked out by Jim. Xander tries then to escape but Jerome finds him. They have a verbal fight, in which Jerome tells he’s disappointed by what Xander told about him, since, in his point of view, all of the things he said were lies. Jeremiah did agree that certain things that he told were in fact exaggerations of the truth. Jerome also tells Jeremiah that he’s going to drive him crazy and then kill him. Jim and Harvey eventually get to them, so Jerome runs away leaving Xander behind. Xander is later taken to the GCPD so that he can be put into protective custody.
Jerome took the Mayor, his wife, and a police officer hostage. He demanded that Jim bring him, Jeremiah and Bruce Wayne. Jeremiah is hesitant to go at first but later agrees. Jerome straps Jeremiah and Bruce into a chair. Jerome tells the crowd the story of him and Jeremiah and then cuts Jeremiah free. Determined to prove Jeremiah is just like him, Jerome hands Jeremiah the knife and tells him to take his best shot. Jeremiah tries to stab Jerome, who knocks him out with a single punch. Later, Jeremiah approaches Jerome’s body after he fell to his death. As Jeremiah walks away, Bruce asks him to let Wayne Enterprises fund his work. Jeremiah thanks Bruce and shakes his hand.
TransformationAfter Jerome's death, Jeremiah discovered a gift in his secret office and opened it. The gift is revealed to be a jack in the box in the form of a disfigured clown head that sprays Jeremiah with a special mixture of the laughing venom created by Jerome. The gas then eventually drives Jeremiah completely insane as Jerome's voice speaks to him in a recording coming out of the gift box, encouraging Jeremiah to be Jerome's successor and his ultimate revenge. Even though Jeremiah tried to fight the venom, it ultimately turned him into a complete maniac with white skin and red lips.
- High-level intellect: Xander is shown to be really smart since he was a kid he used to draw mazes, and when he grew up, after having the best grades at school, he built one in his house, which he built underneath the woods.
- Master tactician and strategist: Using his vast intelligence, Jeremiah also filled his secret hideout with tens of security cameras in order to be ready for his twisted brother's arrival, and using the right tactics to do in order to escape.
- Evasion: While not overly skilled in it, Jeremiah has a degree of skill in evasion, as he was able to evade his brother for years.
- Engineering skills: After graduating school, Jeremiah used his construction skills of labyrinths in order to build a secretive hideout for himself in order to defend himself from Jerome, which took him six years of construction.
- Arrogance: Jeremiah believed that he had captured Jerome and could keep him imprisoned. When Jim and Bullock attempted to put him in protective custody, Jeremiah firmly believed he had defeated Jerome. Only for Jerome to outmaneuver him by leading his allies to Jeremiah's location, hypnotizing his bodyguard, and revealing that he memorized the labyrinths that Jeremiah designed as a child.
- Jerome: Jeremiah's greatest weakness is Jerome, his own twin brother. Since younger age, Jeremiah always suffered from Jerome's twisted and sadistic personality, and he used to abuse him violently and sadistically as one, as Jerome even burnt Jeremiah's bed while he was in it alive. Believing that Jerome's death would now give him freedom, it was revealed that his monstrous brother used him as a pawn in his true master plan; transform his twin into his future revenge, and he indeed succeeded in doing so by Jeremiah inhaling the gas, and he became a white-skinned red-lipped psychopath.
- When Jeremiah is going insane, he clutches his head in a way that mirrors the image of The Joker going insane in the Killing Joke.
- Xander's assumed surname could be a reference to the wild and unpredictable nature of the Joker. It could specifically be a reference to an episode of Batman: The Animated Series called "Joker’s Wilde".