Barbara Gordon, primarily known as Batgirl is an ally of the Dynamic Duo. She operates separately from them but when she appears they work together as the Terrific Trio. She is the daughter of Commissioner Gordon.
Barbara Gordon is the daughter of police Commissioner Gordon. By day, she works for the Gotham Library; by night, she battles the under the alias of Batgirl. Barbara lives in a private townhouse near Gotham's trendy Park Ridge. A service lift in Barbara's bedroom closet runs down to the secret basement where Barbara stores her Batgirl crimefighting gear. In addition to costumes and weapons, the basement also serves as garage for Batgirl's highly advanced Batgirl-Cycle.
Barbara Gordon lived a normal life like any other young adult until she finished college and returned home to Gotham City. It was then that she decided to lend a hand to the cause of justice, perhaps inspired by her father's tales of the Dynamic Duo's exploits. Creating her own costume (she later won an award for best-dressed crimefightress in Gotham City) and Batgirl-Cycle, she took the name Batgirl. A hidden button under her vanity activates a secret revolving door in her bedroom, which leads to the Batgirl-Nook. From there, the 'Domino Daredoll' would don her ginger wig and change into the Batgirl costume. There is also another door, leading to the Batgirl-Cycle, which exits the building through a secret freight elevator.
This "supremely feminine scourge of all that is criminal" seems to have some mechanical knowledge, and she is an accomplished fighter, though she mostly kicks and rarely uses her hands. Her sleuthing quickly brought her into contact with the Caped Crusaders, which led her to develop a crush on Batman. At first, he tried to discourage her from such activities, partly because she was a woman. He was sometimes known to say that she should "leave the crimefighting to men." Undaunted, Batgirl continues to give aid to Batman and Robin whether they want it or not.
The only person who knew her true identity was Alfred the Butler, who discovered her secret identity by accident when he was helping out Batman. He promised her "on (his) word as a gentleman's gentleman" that he would never reveal it. Alfred also never let on that he was confidant to Batman and Robin as well, giving occasional tips to Barbara Gordon/Batgirl via presumed "overhearing" of "rumors".
She has often given great assistance to the Dynamic Duo, and they are most of the time very grateful for her help. They appreciate and honor her secret identity (despite Robin's early protests to the contrary) just as she appreciates theirs.