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.