Historically,
She was assigned the undesirable task of taking care of the Joker — an assignment that would change her life forever. In some versions of Harley's origin story, she becomes infatuated with the Joker because he's one of the only few people that seems to actually care for her.
The Joker does not reciprocate her love and is in fact incapable of romantic emotion as he sees people only as tools to further his own plans. Harley is in denial of this fact and prefers to view him as an antihero until she eventually has to come face-to-face with his complete disregard for her.
History. Joker Jr. was born after The Joker, who had manipulated Harley Quinn into re-entering a life of crime, impregnated her without her knowing.
In the story, the Joker takes Harleen Quinzel to the chemical plant where he originated and pushes her into a vat of chemicals against her will, which bleaches her skin and drives her insane, resulting in her transformation to Harley Quinn, similar to the Joker's transformation in his origins.
In 2011's Suicide Squad comic series, Harley Quinn got a new, expanded origin story in which The Joker tosses the psychiatrist, struggling against him, into a vat of acid, which dyed her skin white and also made her insane.
Best known as the former girlfriend of the Joker, Harley suffers from multiple personalities, homicidal tendencies, Stockholm syndrome and possibly “shared psychotic disorder.” A survivor of domestic violence (not surprising, given her former beau), she has murdered grown-ups and kids.
Lucy Quinzel is the daughter of the Joker and Harley Quinn and the niece of Delia Quinzel.
Believe it or not, this tale saw the Clown Prince of Crime himself become pregnant and give birth to a child. The mother of the child? That was none other than DC's famous magical hero Zatanna, who cast a spell on the Joker after he tried to persuade her to start a family with him.
For example, a DC comic character by the name of Duela Dent went by the moniker "Joker's Daughter" for a bit, alleging the iconic clown was her father. However, that turned out not to be the case. She was then revealed to actually be the daughter of Batman villain Harvey "Two-Face" Dent, at least for a while.
Harley Quinn season two ends with Harley and Ivy finally accepting their feelings for one another and pursuing a romantic relationship.
Harley Quinn started gave the Joker the nickname of Mr. J when she was still a pyschiatrist at Arkham Asylum. She also often calls him Puddin.
Harley Quinn calls the Joker "puddin'" because he gave her a pudding cup when they first met.
After a breakup, Harley Quinn saw how Joker got on without her. His poor lifestyle revealed that Joker might have needed Harley more than he thought. It looks like that between the two, Joker was worse off after his breakup with Harley Quinn than she was without him.
Harleen became obsessed with her subject, and after falling madly in love with the Clown Prince of Crime, she helped him escape the asylum. Her love for the Joker inspired Harleen to adopt a new identity, that of Harley Quinn, the Joker's sidekick-slash-love interest—whether he wanted one or not.
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.
Bethany (aka Beth) is a minor character of Harley Quinn and is the girlfriend of the Joker.
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.
Lucy Quinzel is the daughter of Harley Quinn and the Joker.
Yes, Harley had a daughter whom she let her sister raise. She left the Joker for a year to have said child because she feared that that learning he is a father would lead to a worsening in the Joker's mental state. Her name is Lucy.
In it, Schumacker clarified that they're staying firm on Harley and Ivy's relationship, instead of getting back with the Joker. For me, we still have the occasional fan reaction of “I don't like Harley and Ivy together. She should get back with the Joker,” which we're never going to do.
At the same time, as I have stated, Arthur has the symptoms of psychopathy. Although psychopathy is not among the ten official personality disorders listed in DSM-5, it is well recognised as a variant of antisocial personality disorder (301.7, according to DSM-5).
Harley seems to qualify for HPD, and the over-sexualisation of herself could indicate trauma of a sexual nature from a young age. She also likely has ADHD or another attention based disorder and is struggling through a lot of trauma.
Although Joker is never diagnosed with any specific psychological disorder in the film, his symptoms indicate that he has delusional disorder, bipolar disorder, and pseudobulbar affect.