Duela Dent is a former member of both the Teen Titans and Titans East and also claimed to be the daughter of many Batman villains, though she leans towards being the Joker's daughter.
Duela Dent first appeared as Joker's Daughter. She gained the attention of Robin, as she later claimed to be the daughter of Catwoman, Scarecrow, Riddler, and Penguin. She deduced Robin's identity and he revealed that she was Duela Dent, Two-Face's daughter.
Duela claimed she wanted to join the Teen Titans to atone for her father's crimes. Not everyone was in favor of this idea. She changed her identity to Harlequin. As Harlequin, Duela utilized gimmicks such as smoke-inducing powder puffs and bullet-firing lipstick.
She popped up assisting Batman, calling herself Card Queen while infiltrating a criminal organization called MAZE.
Duela appeared as a guest at Donna Troy's wedding where she appears to be a middle-aged matron. Dick Grayson notes that he'd finally realized she was too old to be Two-Face's daughter, which she agrees with, but disappears before he can take the matter further.
There is some debate about, in pre-Crisis continuity, whether or not Duela Dent was too old to be Two-Face's daughter, since Two-Face was a contemporary of Batman, who was in turn a contemporary of Wonder Woman, who rescued Donna Troy when the latter was an infant. Since Donna is thus young enough to be Wonder Woman's daughter (although she is not), Duela is young enough to be Two-Face's daughter.
On the other hand, there is the fact that Duela had to have been born after Two-Face's debut (since he rejected Duela at birth because he'd wanted twins) and Two-Face's origin came after Dick Grayson's debut as Robin, so there is no way she can be older than Dick Grayson, yet clearly is.
Harlequin aided the Titans during the "Technis Imperative," in which Cyborg's automated system seeks out all Titans allies, past and present. Although she is in a mental institution, Duela is rescued by Cyborg and helps battle the Justice League for Cyborg's soul.
Duela makes a brief appearance insisting to anyone who would listen that the Titans would soon contact her about membership. She also claims that she is the daughter of Doomsday.
When Gar Logan's obnoxious cousin Matt holds a membership drive for "Titans L.A.", Harlequin crashes the meeting-turned-party with a small group of villains, including Beast Boy's enemies Fear and Loathing, simply because she hasn't been invited. Flamebird and Terra defeat her and return her to The Helping House Mental Institution in Industry, California. How she met up with the dangerous villains with whom she crashed the party is unexplained.
Duela socializes with several villains at their secret satellite headquarters and makes a series of wild claims regarding her parentage, all of which are dismissed by the nonplussed villains (she claims that she has been resuscitated by a Lazarus Pit and that her mother may actually be the villainous parent).
Duela returns to action alongside the assembled Titans who face Dr. Light.
One Year Later
The Joker's Daughter and Enigma both serve on the Teen Titans during the year after the Infinite Crisis. Duela is later a member of the splinter group Titans East.
Miss Martian and Cyborg arrive at Belle Reve prison to question their former team mate Bombshell, who has betrayed the team. Risk and Batgirl arrive, and Batgirl murders Bombshell by slitting her throat with a razor sharp batarang. Duela and Enigma cut the prison's power supply, allowing the inmates to escape and attack Miss Martian and Cyborg.
During the attack, Enigma comments to Duela: "Wait'll dear old daddy gets a load of us!"
The two are the captors and tormentors of Raven, whom they torture psychologically. Duela reveals that she joined Titans East simply because they asked. Raven points out that Duela has always been an ally of the Titans, and offers her membership on the team. Duela accepts the invitation by punching Enigma, and fights alongside the Titans against Titans East. When the battle ends, Duela and Batgirl disappear.
Death and Origin
Duela later abducts a teen celebrity from a nightclub, only to be stopped by Jason Todd. She claims that she comes from an alternate Earth. After escaping, Duela is killed by a Monitors, who states, "This world is not yours. Your presence in it is not tolerated. The penalty is death." When informed of Duela's death, the Joker says he never had a daughter. The Monitor of New Earth suggests that Duela's father is actually an alternate version of the Joker, indicating "She didn't belong [...] making others think she was the Joker's daughter. Which on that world, she most certainly was not." Nightwing, Robin, Donna Troy, Wonder Girl, and Ravager set out to investigate Duela's death, but their inquiries are cut short by one of the Monitors, who diverts their attention elsewhere.
It is later revealed that Earth-3's heroic version of the Joker, the Jokester, is the father of Duela Dent, and that her mother was Evelyn Dent, Three-Face (the Earth-3 version of Two-Face). She was raised by Three-Face and her stepfather, the Earth-3 Riddler, and together the three formed the Riddler Family. When she was finally introduced to her birth father, she dropped cryptic hints implying that she or her consciousness shifts unknowingly from Earth to Earth, which is the source of her parental confusion. When the Jokester joined the Riddler Family, Duela revealed that she had been in a relationship with Talon, Owlman's teenaged sidekick. The Jokester renounced her as his daughter and Duela left with Talon moments before the Crime Society stormed their apartment. The Riddler was killed by Ultraman and Three-Face's arm was torn off by Superwoman; the Jokester managed to flee until he is later tracked down and killed by Solomon, the Monitor who killed Duela.