Warning: Spoilers for DC Comics' Harley Quinn #2!
Before the villainous Joker arrived on the scene to torment Batman, there was another recurring foe for the Dark Knight: Hugo Strange, who's returning with a long-term agenda in the second chapter to Stephanie Phillips (Descendent, Superman Man of Tomorrow) and Riley Rossmo (Cowboy Ninja Viking, Constantine The Hellblazer)'s all new Harley Quinn series.
Reformed supervillain Harley Quinn makes her return to Gotham City right in the midst of a monumental new development. In order to help pull the city back from the brink, Gotham Mayor Christopher Nakano employs former villain Dr. Hugo Strange to restore the "great city" to its former glory, following the ramifications caused during 2020's Joker War event.
Seemingly reformed, Strange is appointed the head of Gotham's newfound rehabilitation program S.A.F.E. (Secure And Fearless Engagement Program), appropriately housed in mainstay psychiatric hospital Arkham Asylum. In an effort to undo the damage left by the Joker, S.A.F.E. is aimed at the reformation of chaotic clowns throughout the city, including Harley Quinn. In the eyes of Nakano, Strange's status as a former criminal himself makes the experienced doctor an ideal candidate to oversee a project as ambitious as S.A.F.E. At first glance, Hugo Strange seems to be playing along with Nakano's program to meet the needs of Gotham's citizens by cracking down on the crime caused by the Joker, but it's all a part of Strange's own ulterior motives.
Harley's inability to be reaccepted into society shows that Hugo Strange is benefitting from an asset that few Batman antagonists lack: a colorful costume or heightened abilities. Strange looks to use this foothold to his advantage in ridding Gotham of not only costumed villains but residents in need of a change to their general life decisions. Though Hugo Strange is very much a recognized figure in the world of Gotham, in appearance he is like any other citizen, as opposed to having any distinctive facial scars or masks. This is perhaps what makes Strange stand out amongst the Dark Knight's famed rogues gallery.
In his first comic appearance with April 1940's Detective Comics #36 by Batman creators Bob Kane and Bill Finger, Strange challenged the titular hero and proved to be a threat to Batman even without powers. Detective Comics escalated the new foe from a one-off character to a recurring threat, until the addition of the Joker two months later gained more attention, due to the character's distinct appearance and playful yet deadly gimmicks. Following the Joker would then come Two-Face, Poison Ivy, Riddler, and Penguin, marking Batman's turn to costumed supervillains. While the Joker may have succeeded the good doctor in popularity, Strange's subtlety is ultimately what placed him in the good graces of Mayor Nakano and pushed other reformed criminals like Harley by the wayside.
Briefly glimpsed through a pair of round glasses, the real monster is within Strange. While Strange has occasionally donned a cape in the past, it's out of his obsession with Batman, not out of a need to do good. It can be reasoned that Hugo Strange's lack of flashy effects and costume has prevented the character from making his debut in a live-action feature film, despite his massive genius and cunning that rival both Harley Quinn and Batman.