The Harlequins of Two Earths: Duela Dent and Molly Maynne

Duela Dent began her costumed career impersonating the daughters of various supervillains from Gotham City. Earth-One's Robin and later Batgirl repeatedly faced Duela in her aliases as Joker's Daughter, Catgirl, Scarecrone, as well as the daughter of the Riddler and Penguin. Each of these forays into criminality were staged ahead of time, allowing Dent to engage in and impress the ex-Boy Wonder. Her ultimate goal was to become a member of the Teen Titans, which she soon became during their initial incarnation. 

Molly Maynne began her costumed career adopting the alias of the Harlequin. A secretary for radio announcer Alan Scott at Gotham City radio station WXYZ, she developed a romantic crush for Scott's alter ego the Green Lantern, who was focused on his career as a crime fighter. Seeing this as the only way to attract his attention, Molly employed her illusion generating eyewear, trick mandolin and stylized car as a supervillian. However, rather than having evil intent, Harlequin ended up often working alongside Green Lantern in defeating her criminal henchmen.

Duela eventually joined the Teen Titans, adopting her most notable alter ego as the Harlequin, where she served alongside that team for a number of adventures. When the Titans eventually dissolved, Dent infilitrated the evil  organization known as M.A.Z.E. as the pseudo-crook known as the Card Queen. After helping Robin in defeating this gang, Duela finally retired from her superheroine escapades, and later reunited with Robin and the Titans during their teammate Wonder Girl's wedding. Duela's true origins remained a mystery. 

Molly eventually was recruited in the Injustice Society, and when she betrayed them to aid Green Lantern and his Justice Society allies, she distanced herself from other supervillains. She later on became a secret government agent in the late 1940s and early 1950s, and decades later reunited with Green Lantern when she helped him defeat his former wife, Rose "Thorn" Canton. Following her death, Molly and Alan finally wed as husband and wife.