Harley raised the Dee Twins herself and it's unknown what happened to their parents. Having given up her allegiance to the Joker, she did her best to ensure that they grew up like normal kids. She failed, as Delia and Deidre inherited Harley's earlier fascination with the Joker. The twins joined his namesake gang while still in their early teens. They are identical and impossible to tell apart: both have long blond hair and blue eyes. Their attire consists of red Raggedy Anne-like wigs, white hats, red strapless tops, white shorts, red go-go boots, and clown makeup.
Dee Dee, along with Bonk, Chucko, Woof, and Ghoul, were recruited by the resurrected Joker for his plan to attack Gotham City. On his orders, the Jokerz stole advanced technology from a series of warehouses.
In the gang's first confrontation with Batman, the young Dark Knight made the mistake of taking them for inconceivable and useless girl "helpers". As soon as he turned his back on them, however, they attacked him with an amazing blend of skill, ferocity, and coordination.
Appearing as their "normal selves," they later attacked Terry in a nightclub, and he barely managed to avoid them.
In the Jokerz' last confrontation at the Jolly Jack Candy Factory, Batman fought smart: first, using his invisibility powers, he goaded them; second, lured them into walking over a floor slippery with jawbreakers; and, third, tricked them into charging into each other knocking themselves out.
The twins were arrested. They were bailed out into Harley's custody while awaiting their trial. Harley ranted in disappointment, "You rotten little scamps! I struggled to make a good home for you, and this is the thanks I get?!" She swatted them on their behinds with her cane as she continued, "Break a grandmother's heart! I hope they throw the book at you!" "Oh, shut up, Nana Harley," the twins responded in frustration.
In an alternate timeline, Dee Dee and the other Jokerz were recruited by Chronos as enforcers, and upgraded with radically advanced technology and weapons, giving them actual superpowers. In this time-stream, Dee Dee reportedly killed Kai-Ro.
In another battle with the Justice League Unlimited, they succeeded in killing Terry as well.
The Dee Dee Twins are very identical in appearance and outfit. Both have grey eyes and long blonde hair, which they hide under yarn-like wigs. Their attires consist of white hats, red strapless tops, white booty shorts, red go-go boots, and harlequin makeup.
Delia and Deidre Dennis, better known as Dee Dee, are thrill-seeking delinquents who inherited their grandmother's fascination with the Joker, and joined his namesake gang for kicks, and possibly personal gain through street crime.
Although they are two individuals, as twin sisters, they appear to act as though they are one person in two bodies, often speaking as one or completing each other's sentences, along with the fact they are co-referred to as Dee Dee. In fact, they always address each other as Dee Dee, and the way they speak to the other sounds very similar to a person talking to him or herself. They do care for each other and are willing to abandon a job to help the other, as during their first encounter with Batman, one broke away from helping to carry a large piece of technology to save her sister from falling to her death.
Besides their trouble-making ways, they are also definitely cruel and deceitful, shown when they pretended to be afraid of Batman (Terry McGinnis) and viciously attacked him the moment he turned his back on them, as well as how they had no qualms harming the elderly Bruce Wayne.
In the alternate timeline, they proved themselves to be murderous, having killed members of the Justice League.
Despite their impressive teamwork by acting as one person, they are still susceptible to sibling-rivalry, as Terry tricked them into fighting each other. Moreover, they are followers, not leaders, shown when they cowed in the presence of the Joker, as well as Chronos.
Powers and Abilities
The twins were shown to be very skilled Olympic-level gymnasts and experts at tumbling and are ok at hand-to-hand combat, though not nearly on the same level that their grandmother was.
In the alternate timeline, the twins were granted metahuman powers by the time traveler Chronos that allowed them to multiply themselves upon kinetic impact, and carried powerful energy whips capable not only of releasing said energy into targets ensnared in them, but which also had the ability to pierce the shields and constructs of Green Lanterns with ease (as they were yellow).