WARNING: The following article contains spoilers for Heroes in Crisis #3 by Tom King, Lee Weeks, Clay Mann, Tomeu Morey and Clayton Cowles, on sale now.
Harley Quinn turned 25 this year -- as a comic book character, that is. She made her comic book debut in 1993, in Batman Adventures #12, becoming the Joker's sidekick and love/hate interest. More recently, though, Harley had expanded beyond the Bat-verse and into the rest of the DC Universe proper, via her role as a member of the Suicide Squad.
Tom King and Clay Mann's Heroes in Crisis appears to be further expanding her influence. In Issue 2, she managed to get the drop on not only Batman, but Superman and Wonder Woman as well. And in Issue 3, she appears to coldly murder Wally West. Harley had already transformed from a second-rate villain into more of an antihero, but killing The Flash reverses that path and casts her as an outright villain. Is that perhaps Harley's next role, not only moving back to the role of a criminal, but also instated as one of the DCU's premier threats?
Harley's Humdrum History
In Batman: The Animated Series continuity, Harley was often cast as comic relief, in contrast to the Joker's comedic but darker tendencies. When her character was copied into the more serious mainstream DC continuity, she was given a little darker personality to match. Her presence was largely contained within the Batman family of titles, however, until DC's New 52 incarnation of Suicide Squad. She eventually graduated into her own series by Amanda Connor and Jimmy Palmiotti.
When she was in the shadow of the Joker, Harley never really stood out as a potential threat on her own. As a pseudo-hero, she likewise never had a place at the table among heroes like the Flash or Green Lantern. Whether one of the good guys or bad, the name Harley Quinn was never really bandied about with any kind of distinctiveness or significance. Although popular with readers, her character always seemed confined to the fringes of the DCU, never really playing a part in any truly major events.