Harley Quinn

Harley Quinn is one of the main antagonists of the Batman animated series and franchise as a whole. First introduced as a cartoon original villain in the original animated Batman series, she grew popular enough to have appearances in the comics and eventually became one of the mainstay staples of the franchise as a whole. Really, she's the OG sexywoman. As said in the Sexywomanpedia, "she ran so Vriska could walk."

Basic Information
Harley first appeared in the episode Joker's Favor, where she really didn't play much of a role at all, nor was her backstory expanded on. We only got to see her backstory an entire season later, with Mad Love. At first a normal psychologist, when she spent some time interning at Arkham Asylum, she took a particular interest in the Joker, setting up several therapy sessions with him. From there, the Joker manipulated her by creating an elaborate backstory to gain her sympathy, eventually turning her mad and making her into the villain she is today.

For more information, see her page on the Batman wiki.

Angst
The Joker is. Not a very good boyfriend, to say the least. She gets better after she leaves him, though.

Chaoslord/Clown
As is to be expected of someone created as a girlfriend for the Joker, she has both chaos and clownery in spades. Her more modern portrayals tend to lessen the clown aesthetic in favor of the chaoslord aesthetic, though.

Distinctive Voice
Her Brooklyn accent and particular use of slang make a voice that's hard to mistake for anything else.

Fuck The Joker
HarlIvy is the ship this trope is named after, and one of the primary examples of how spite can come into play with these kinds of ships.

Girlboss
You look at the animated series starring and named after her, and tell me people give a shit that she's a criminal.

Intelligence
Licensed psychologist! Humorously, some of her animated portrayals have had her retain at least some level of attachment to the title, if not her skill as a psychologist entirely. She may be a criminal, but that doesn't automatically erase those years she took to get a degree.

Knifemurder
Has no issue killing people, as is the case with most Batman villains.

Villain
Yeah.

WLW
In a relationship with Poison Ivy in both the comics and the Harley Quinn animated series.