That's right: Batman and Joker are half-brothers, at least according to Penny. The movie never explicitly makes clear whether that's true or not.
However, in the wider DC Universe, the Batman and Joker are not brothers and never were.
Image via Warner Bros. Key to Arthur's spiral is new information he learns from his mother Penny (Frances Conroy), with whom he lives. Arthur finds a letter Penny has written to Thomas Wayne, claiming that Wayne is Arthur's real father.
In Joker, Thomas Wayne (Batman's father) and Penny Fleck (Joker's mother) are key characters. Penny claims that Thomas is actually Arthur's father.
Penelope "Penny" Fleck is the deuteragonist villain of the 2019 psychological thriller film Joker, the first installment of the DC Black film series. She is the adoptive mother of Arthur Fleck, a mentally unstable failed comedian whose lack of success and respect triggers his transformation into the Joker.
As we come to learn, not only was Penny a Wayne employee, but she claims she and Thomas were lovers and that he is Arthur's father. That's right: Batman and Joker are half-brothers, at least according to Penny.
She is the wife of Thomas Wayne and the mother of Bruce Wayne. Joe Chill murders Bruce Wayne, rather than the boy's parents. Martha Wayne was so traumatized by the event she becomes the Joker. Her husband Thomas wished to gain revenge for his son's murder and becomes this reality's version of Batman.
In Batman's origin story, Joe Chill is the mugger who murders young Bruce Wayne's parents, Dr. Thomas Wayne and Martha Wayne. The murder traumatizes Bruce, inspiring his vow to avenge their deaths by fighting crime in Gotham City as the vigilante Batman.
In Injustice: Gods Among Us, Harley Quinn reveals she gave birth to Joker's daughter, but gave her up for adoption rather than subject her to a life with Joker as a father. Similarly, Harley becomes a mother to twin children in the Batman: White Knight universe, though with happier results.
On antimatter Earth, Owlman was now Thomas Wayne Jr., the older brother of that reality's Bruce Wayne. In most mainstream DC universes, Batman's genesis occurred when young Bruce Wayne was witness to the murder of his parents, and was inspired to devote his life to fighting crime.
Joker and Batman are not brothers, even though the movie suggests that they are. It is later revealed that Arthur is, in fact, adopted, and his true origins are unknown.
As he confronted his mother, Harley's allies found her and informed her that they had found Joker's body. Joker Jr. then revealed himself to be Harley's son who she had abandoned as an infant.
The psychopathology Arthur exhibits is unclear, preventing diagnosis of psychotic disorder or schizophrenia; the unusual combination of symptoms suggests a complex mix of features of certain personality traits, namely psychopathy and narcissism (he meets DSM-5 criteria for narcissistic personality disorder).
Damian Wayne is the biological son of Bruce Wayne (Batman) and Talia al Ghul. His existence was hidden from his father up to when he was about ten years old, during which time he was trained by the League of Assassins in a variety of disciplines to make him an extremely efficient killer.
One of the biggest secrets in the world of DC Comics has been revealed as one of its most iconic characters, an enigmatic villain, gets an official name. In the latest issue of Flashpoint Beyond #5, the Joker's real name has been revealed: Jack Oswald White.
Penny Fleck was the adoptive mother of Arthur Fleck, a mentally unstable failed comedian who would later call himself the Joker. Much like her son, Penny suffered from an unspecified mental illness.
Jeremiah Valeska is a major antagonist in the television series, Gotham. He is the twin brother of the terrorist cult leader, Jerome Valeska, as well as being the arch-nemesis of Bruce Wayne. Jeremiah is the show's equivalent to the Joker, taking over from Jerome, although both of them never took on the Joker alias.
Each twin adapts different characteristics of the DC Comics supervillain the Joker. Jerome is depicted as a chaotic, nihilistic character who spreads chaos in Gotham City until his eventual death, while Jeremiah is a cunning psychopath obsessed with tormenting Bruce Wayne.
In the different forms of Batman media, Batman and the Joker are depicted as being enemies because they have opposing goals within Gotham City. While Batman is trying to save the city from its own darkness, the Joker enjoys causing further chaos.
Dick Grayson, the original Robin, gets word that Batman snapped and killed the Joker. He goes back to Gotham to confirm this, and sees the body himself. It's just a mangled corpse out of view, but fans know the green hair anywhere. Unfortunately, the series undermines that resonance by the end.
The most common story involves him falling into a tank of chemical waste that bleaches his skin white and turns his hair green and lips bright red; the resulting disfigurement drives him insane. The antithesis of Batman in personality and appearance, the Joker is considered by critics to be his perfect adversary.
Napier was charged with assault with a deadly weapon at age 15. As a young man, Napier and his accomplice Joe Chill rob and murder Thomas and Martha Wayne in the alleyway behind the Monarch Theatre, leaving their young son Bruce as the only survivor.
Joker's original idea was revealed in Jim Starlin and Jim Aparo's legendary Batman: A Death in the Family. After beating Robin half to death with a crowbar, Joker tries to use a bomb to not only kill Jason, but to also wipe out any and all evidence of Joker ever having been there.
As revealed in the comic Batman Beyond 2.0, Bruce Wayne and Barbara Gordon had an affair while Barbara's boyfriend Dick Grayson was away. Barbara fell pregnant.