Unlike many of Batman's villains, Harley Quinn did not originate from the pages of comics, but rather from the Batman: The Animated Series season one episode, "Joker's Favor." She wasn't intended to be a long term adversary to the caped crusader, but fans adored her so much, she returned to become a regular character.
That isn't to say she hasn't seen a significant number of changes as the years have progressed. Between her first introduction until now, the differences have been staggering, and it's time to explore what they are.
10 Skill
Since she delved the treacherous path from therapist to maniac, Harleen Quinzel's skills have noticeably improved. She is able to physically defeat the Joker in combat, annihilate squads of police officers and legions of the Enchantress's monsters, and can even anticipate, and block punches from Batman himself.
This is a stark contrast from her initial debut, where she could barely hold her own against Robin even if she had successfully ambushed him. Her growth in skill may be attributed to more experience, though it is also congruent with her evolution as an individual.
9 Her Relationship With The Joker
Initially created as an asset to enrich the Joker's own character, Harleen has slowly but surely come into her own. The story of a woman who fell for a troubled criminal would become a tragedy from the years of abuse he inflicted upon her, though it would not remain that way.
Harley has broken off from the Joker, recognizing the evil ways he had mistreated her. Despite this development, she remains unhinged and at large, proving a cautionary tale for young lovers everyone; your choice in a partner may define you.
8 Aesthetics
Harley's outfit and overall appearance have changed a lot, and it's symbolic to her status as an independent woman. Her previous outfit, chosen by the Joker, was tight and elastic, much like a gymnastics outfit. It was in the likeness of a jester, reflecting Quinn's status to the Clown Prince; she was a novelty to amuse him and nothing more.
Newer iterations including those from Birds of Prey, Suicide Squad, and even her independent show have given her a more provocative, free-spirited design, from her mismatching eye shadow to her somewhat maroon booties and even her decorated bat.
7 Adversaries
Becoming independent would not be without its drawbacks. Where Quinn once only had to contend with Batman and Gotham's authorities, her newfound freedom presented new problems and perils. Naturally, many of these dangers stemmed from the Joker himself, sore at his loss of a plaything.
However, a widened selection of enemies also presented Harley with different challenges to adapt and overcome. While she may never defeat Batman in an even fight, she proved more than capable of dispatching the same threats he did, even taking several on at once.
6 Leadership
While Harley may have commanded a handful of Joker's henchmen in the animated series, her leadership nonetheless has dramatically improved alongside her confidence. She was a pillar of strength for the rest of the group as Deadshot or Flagg in Suicide Squad and led her own party on a mission in Birds of Prey.
Though she operated under the coercion of Amanda Waller, the initiative and tenacity Harleen displayed insinuated a deeply rooted strength and natural charisma which the members could rally behind.
5 Motivation
Harley Quinn's early motivation was a depressingly simple one; she wanted to make her Puddin' happy, and she would go to any lengths to appease him. Consequently, she suffered abuse, imprisonment, and misery on his behalf ~ sometimes directly from the Clown Prince himself.
In recent years, she has demonstrated a new drive: freedom. Though this might often manifest as crime from when she and Batman come to blows, it is an aspiration borne of defiance. This opposition is not against the system Harley has grown to disdain, but to the Joker himself. Her autonomy makes him bristle with rage, and she relishes every second of it.
4 Perception
When working as the Joker's favorite hench girl, Harley was scarcely a footnote in the eyes of those her boyfriend rubbed elbows with. It wasn't uncommon for villains like Black Mask to use women like her as symbols of his own power, and thus she was often dismissed.
Quinn has demonstrated otherwise. From exhibitions of ruthlessness to taking on Killer Croc and winning, none would dare to presume her any lesser than her victories have demanded. Now, she is viewed as an equal among rogues and a concern to the heroes, should she ever feel mischievous.
3 New Standards
Pamela Isley has helped Harley Quinn grow in more ways than one. In addition to imbuing her with newfound strength well surpassing ordinary human limitations, she has also given her a healthier relationship to explore.
The effort isn't exclusive to Ivy. After Harley's final breakup with the Joker, she began holding the people she surrounded herself with to a higher standard, respecting others only when they respected her (and sometimes, not even then). She no longer entertains manipulation, whether from Batman, her ex, or anyone else.
2 Weapons
Over the years, Harley Quinn has grown familiar with a small arsenal of weapons as her criminal career became more prolific. This not only proves a versatile advantage in any given situation, but it also plays into her greatest strength of unpredictability, much like the Joker.
In the beginning, she had only her mallet and, occasionally, a small revolver. Since then, she has experimented with a wind-up boxing glove gun, the Joker's laughing gas, knives, bombs, and even an exploding pie. Quinn has also progressively began to utilize her hyenas more often, lovingly named Bud and Lou.
1 Role
This is perhaps the most significant way Harley Quinn has evolved over the years. Where once she was a tragic villain and part-time antagonist, she has now stolen the role of protagonist and unlikely heroine, working as an unlikely agent of good in many of her latest depictions.
Her latest position as a hero is both a redemption arc and a unique speculation on what defines a hero and villain. Harley's story is one that continues to intrigue and fascinate, keeping avid fans speculating as to where she might ultimately end up. Given that she would later become the ashamed grandmother of the Dee Dee twins in Batman Beyond, it's safe to assume she'll eventually commit to heroism full time.