Most of the time when Arthur laughs, it isn't because he wants to. Arthur has a condition, a real condition, that makes him uncontrollably laugh when in moments of extreme distress. The laughter comes out with such force that it actually chokes him, causing him to almost regurgitate the laughter.
Personality disorders. In general, Arthur appears to have a complex mix of features of certain personality traits, namely narcissism (since he craves attention by any means) and psychopathy (since he demonstrates no empathy for his victims).
What mental illness does the Joker have that makes him laugh?
The above-mentioned characteristics make the Joker's laughing episodes compatible at first sight with the pseudobulbar affect, a clinical entity characterized by episodes of exaggerated or involuntary expression of emotions, including uncontrolled laughing or crying.
While the movie never names what specific illnesses Fleck has been diagnosed with, these fits of controllable laughter are based on an actual disorder called Pseudobulbar Affect, or PBA.
Later, Arthur goes to Arkham State Hospital and steals his mother's records, and finds out that he was in fact adopted, and that Thomas Wayne is not his father and that Penny is not his true mother.
WHY DOES ARTHUR KEEP RETURNING? | RED DEAD REDEMPTION 2
How does Joker's mom know Thomas Wayne?
I asked Todd how Thomas Wayne would've know Arthur's mother. The backstory was that Arthur's mother had worked for Thomas in his home, and she was a beautiful woman who Thomas was attracted to and it led to a physical relationship. Later in life, she's in and out of mental institutions.
The Joker (or Arthur) appears to have a complex mix of diagnoses, including pseudobulbar affect – a rare condition consisting of uncontrollable laugher or crying, and possibly a psychotic illness, evidenced by his apparent hallucinations about the subject of his affections (played by Zazie Beetz).
In the documentary I Am Heath Ledger (via Digital Spy) it's revealed that, in order to keep the prosthetics in their place as they got loose when he spoke, Ledger had to lick his makeup to keep it in place, and it ended up becoming part of the Joker's manic personality, as well as his most memorable mannerism.
Director Todd Phillips considered the character's body size as one way to represent his vulnerability. It is important to emphasize that unlike most people who diet to lose weight or who develop an eating disorder, Phoenix's weight loss was intended for the short amount of time it took to shoot the movie.
Originally Answered: Why did Joker kill his own mother? Because his mother lied to him about the fact that Thomas Wayne wasn't his father. After stealing some files from Arkham, he finally learned that he was adopted, and that his mother abused him maliciously as a child.
Personality Disorder, specifically, Histrionic Personality Disorder plays a key part in Harley Quinn's life. People with Histrionic Personality Disorder are “pervasive and excessive emotionally and display attention-seeking behavior” (Bornstein 1998).
The Joker has undergone many revisions since his 1940 debut. The most common interpretation of the character is that of a man who, while disguised as the criminal Red Hood, is pursued by Batman and falls into a vat of chemicals that bleaches his skin, colors his hair green and his lips red, and drives him insane.
Much like her son, Penny suffered from an unspecified mental illness. She was responsible for letting her former boyfriend abuse Arthur in his childhood and was temporarily sent to the Arkham State Hospital for unsolicited claims.
To get into the character of Arthur Fleck, Phoenix lost 52 pounds for the role by eating a restrictive diet that was supervised by a doctor. Phoenix said the weight loss gave him a sense of control and the confidence to dig deep into the Joker's persona.
Arthur has a neurological condition that causes him to laugh involuntarily, which the film suggests may stem from a traumatic brain injury caused by childhood parental abuse. Throughout the film he experiences undefined psychiatric symptoms that include paranoia, visual hallucinations and delusions of grandeur.
The Joker then finally says "See you in Hell!., before, in a last act of revenge against his enemy, twists his neck just far enough to kill himself, committing suicide and framing his enemy for his own murder.
When the Joker became obsessing over destroying the Bat-Family, he decided to arrange for his face to be surgically removed. According to the Joker, he did this to symbolize how even without his, "Mask" he was still the joker where-as Batman's Robins and Bat-Girls' identities were only mask-deep.
He taunts his victims with pseudo stories of trauma in order to ramp up the tension before he inevitably gets his laugh by maiming or killing someone. The origin of his scars remains a mystery because the Joker doesn't care about how he got them anymore; he merely cares for the effect they have invoking fear in people.
Also in those records are some newspaper clippings that reveal Arthur was three years old when the authorities learned that his mother's boyfriend abused them. This puts Arthur's birth year in 1948 or 1949, meaning that he was 32-33 years old during the events of the film.
Arthur Fleck, later known as the Joker, is a failed comedian who, following his great lack of success and respect, loses his mental stability until he becomes a nihilistic, sociopathic killer calling himself Joker, aiming himself to make Gotham smile in his way.
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).
There's no story where the Joker and Batman are brothers. The only supposed brother batman may have is Lincoln March, who claims Martha Wayne gave him to an orphanage before she had Bruce and claimed his official name is Thomas Wayne Jr but that's never been proven and it's kinda forgotten.
It is then revealed that the Joker's real name is "Jack Oswald White." Martha then shares that she visited the Flashpoint universe's version of Jack Oswald White, discovering him to be a struggling family man supporting his wife and a child as a janitor at Wayne Casino.
