Jeremiah Valeska

Jeremiah Valeska, also known as Xander Wilde, is the final antagonist in the fourth season of the TV series Gotham. He is Jerome Valeska's twin brother and is the show's version of The Joker.

He is portrayed by Cameron Monaghan, who also portrayed Jerome.

Origins
Jeremiah and Jerome were identical twins, and one day, their mom sent them both away, knowing that Jerome will be evil. Jeremiah becomes a very high skilled engineer during life, and he has a proxy working for him. He also changes his identity to Xander Wilde, in order to protect himself from Jerome.

Escaping Jerome Valeska
Jeremiah later sends his proxy Ecco to capture Jerome so he can be held inside a cage. Jim Gordon and Harvey Bullock ask him to hand Jerome to the GCPD, but Jeremiah refuses. Jerome however hypnotizes the proxy and sends her to kill Jim Gordon and Harvey and to bring Jeremiah to Jerome. Jeremiah is taken to his brother, who confronts him with Jervis Tetch and Jonathan Crane, and tells him that he will turn insane and then die. Jim Gordon however starts shooting Jerome, thus chasing him away, and saving Jeremiah.

Creation of the Joker
Jerome later kidnaps Jeremiah and tries again to convince him that he is mad. Jerome, however, claims that Jeremiah is just as crazy and always has been, and that it's in their blood. He gives Jeremiah a knife and dares Jeremiah to kill him. Jeremiah tries to do so, but is kicked on the head by Jerome, who then tries to kill him.

Later, Jerome dies, and Jeremiah thanks Bruce Wayne, Jim and Harvey for helping him save the city. He gets a gift from The Wayne Enterprises, which actually contains one of Jerome's traps. The trap sprays laughing gas on Jeremiah, who has his hidden insanity and psychopathic tendencies unleashed by Jerome. as his skin becomes white and his lips become red, to become The Joker and have some "fun".

Personality
Even before becoming the Joker, Jeremiah was quite the suspicious individual. Aside from being the brother of one of Gotham's most notorious criminals, even in his younger days he had a unique interest in designing plans for mazes and traps, and even Jerome claims that Jeremiah is actually crazy like himself, just too afraid to let it show. It is shown that Jeremiah had been dishonest about his brother's attempts to murder him, although he claimed that everyone knew Jerome certainly wanted to do it. He also displays a disturbingly calm manner when held at gunpoint by Gordon and lies about his past with his brother as well as keeps him contained without caring about the GCPD's consent.

If Jeremiah was psychopathic before being exposed to toxin, he did everything he could to hide it in comparison to his brother, who felt as though his revenge on Jeremiah should be to forcefully expose his psychosis by means of laughing gas.

Trivia

 * Jeremiah Valeska is the fifth incarnation of Joker to have an established backstory and identity, with the first one being Jack Nicholson's Joker in the 1989 Batman film, the second in The Killing Joke, the third the Martha Wayne version of the Joker from the 2011 "Flashpoint" crossover story arc, in which she was Joker in an alternative universe where Bruce Wayne was dead (having been killed by the mugger) and Thomas Wayne as Batman, and the fourth being Lovers and Madmen, a Joker comic origin story.
 * Jeremiah's transformation and breaking into laughter is similar to The Joker's breakdown in The Killing Joke following his transformation.
 * This version of Joker in the fourth version to appear on television: the first was in the campy 1960s Adam West Batman television series in which he was played by Cesar Romero; the second was in one of the six Batman OnStar commercials which ran from 2000 to 2002, in which he was played by Curtis Armstrong; and the third was a cameo appearance in the 2002-2003 series Birds of Prey, in which he was played physically by Roger Stoneburner and voiced by Mark Hamill.
 * Jeremiah is similar to Tim Drake from Batman Beyond: Return of the Joker, who was transformed into the new Clown Prince of Crime following the original Joker's demise in order to continue his legacy.
 * He is the youngest version of "The Joker", being around 21-22 years old at the time of his transformation. Also this version comes before Bruce Wayne becomes Batman.
 * When Jeremiah is transforming into the Joker, he makes a very similar pose that the Joker made in The Killing Joke.