Harley Quinn, born Dr. Harleen Frances Quinzel, is one of DC Comics' most iconic and popular characters. Originally introduced as a sidekick and lover to the Joker, she has since evolved into a complex anti-hero, often operating independently or as a key member of teams like the Suicide Squad and Gotham City Sirens. 

Core Origins & Background

• Creation: Harley Quinn first appeared in the Batman: The Animated Series episode titled "Joker's Favor" on September 11, 1992.
• Dr. Harleen Quinzel: Before her transformation, she was a promising psychiatrist at Arkham Asylum.
• Meeting the Joker: She was assigned to treat the Joker but was instead manipulated and seduced by him, eventually falling in love and helping him escape.
• Transformation: In many modern retellings, her transformation is finalized when the Joker pushes her into a vat of chemicals at Ace Chemicals, bleaching her skin and fracturing her psyche. 

Abilities & Equipment

• Skills: She is a highly trained psychiatrist and an Olympic-level gymnast and acrobat.
• Enhanced Physiology: Injected with a special serum by Poison Ivy, Harley possesses immunity to most toxins and enhanced strength, agility, and durability.
• Signature Weapons: She is known for using clown-themed gag weapons, most notably her oversized wooden mallet and a customized baseball bat. 

Relationships & Alliances

• The Joker: Their relationship is traditionally depicted as abusive and toxic, with Harley serving his every whim until her modern "emancipation".
• Poison Ivy: Often her closest friend and romantic partner, Poison Ivy frequently encourages Harley to leave the Joker and find her own path.
• Suicide Squad: Harley is a recurring member of Task Force X, a government-sponsored group of villains sent on high-risk missions.

• First Comic Book Appearance (non-canon): Her first appearance in a comic book was in The Batman Adventures #12, published in September 1993, which was set in the continuity of the animated series.
• First Main DC Continuity Appearance (canon): Harley Quinn was officially introduced into the mainstream DC Universe in the one-shot graphic novel Batman: Harley Quinn #1 in October 1999, which told her origin story during the "No Man's Land" event.
• First Live-Action Film Appearance: Margot Robbie portrayed the character for the first time on the big screen in the movie Suicide Squad, released in 2016.