Doctor Harleen Quinzel is probably most famous for her “mad love” romance with the Joker that prompted her creation in the first place. However, I would posit that Harley Quinn’s greatest partnership—and her greatest romance—is with another iconic Batman villainess. Doctor Pamela Isley is some 40 years older than Harley in publication history, but the two have enjoyed a relationship on any number of levels throughout the 25 years that the Clown Princess of Crime has been smashing hearts with her synonymous mallet.

When I think of a functional relationship, equal partners who bring out each other’s best qualities is the blanket idea that comes to mind. All I have to do is cast my mind back to the Batman: The Animated Series episode “Holiday Knights” when they kidnap Bruce Wayne and go on a shopping spree with the billionaire’s uncapped credit cards.

In keeping with the style of the show the episode is sweet and funny and singularly highlights what makes each of them a true threat to the citizens of Gotham City. For her part, Poison Ivy effortlessly renders Bruce Wayne pliable to their whims, thereby removing any threat to their immediate persons. In the wake of Ivy’s dynamic work, Harley is able to follow her heart’s desire down the path of chaos and destruction that makes her such a force in the Gotham City underworld.

It’s also tremendously clear to me that Poison Ivy is the best thing that has ever happened to Harley Quinn, since she is the only character who has ever cautioned Harley against continuing her relationship with the Joker. I, personally, love a more villainous Harley Quinn, but every once in a while, a girl needs to hear the hard truths and Ivy really rises in my esteem for looking out for her companion in this way. I believe it also speaks to the depth of the bond they do share. Poison Ivy isn’t just dispensing life advice to any wayward child she comes across. This caution comes from her heart.

When Harley Quinn broke out of the small screen and onto the comic book page, her first appearance was in BATMAN ADVENTURES #12 which is set in the same continuity as the Batman: The Animated Series television show and pits the lady in black-white-and-red-all-over against Batgirl. Who should be at Harley’s side, I ask you? It was definitely Poison Ivy! By the conclusion, all three women are forced to work together. It’s an awesome end to an awesome issue.

When Harley ascended to the DC Comics continuity proper in Paul Dini’s BATMAN: HARLEY QUINN #1, the Batman event NO MAN’S LAND was well underway and Harley had been cast aside by the Joker. Poison Ivy took her in and looked after her, injecting her with the same toxin as she did in the cartoon and rendering her with heightened strength and agility.

…Even though, in the end, Harley does go back to the Joker. Again.

By the time of this storyline, the Harley/Ivy dynamic had been repeated three times and was securely in place—so much that the pair became a well-recognized team that would lead to their shared miniseries HARLEY AND IVY (which you must pick up and read if you haven’t yet).

For a relationship to be cemented in less than a decade is pretty remarkable in the comic book publication timeline, and everything for these two builds on the tropes laid out in The Animated Series. For those of you playing along at home, please don’t look at my use of the word “trope” as an insult. Tropes are tropes because they are well-liked and commonly-used and so is the relationship between Ivy and Harley. 

For her part, Harley Quinn brings unpredictability and level of dedication to achieving her goal that both keeps any plan undertaken by her interesting from a reader’s perspective and extra dangerous. She lacks even the base logic that the Joker lays out when he is threatening the lives of innocents. Her ardent support of almost anything that Poison Ivy may be proposing at any given time means that they frequently get the ball rolling on dangerous plans with all speed. Following the almost certain thwarting of their plan at the hands of a member of the Bat family, Harley enters a relapse cycle of love—and common return—to the Joker’s side where she can feel a sense of structure that she is incapable of providing for herself. Ivy’s inevitable caution is thrown to the wind and then the entire cycle repeats itself.