Selina Kyle started life in the destitute East End of Gotham City. She was on the streets by thirteen, parents dead and separated from her little sister who she'd always tried to protect. She learned to steal to survive, refining her skills over the years to become one of the best cat burglars in Gotham City.
A series of interesting teachers left her a world-class fighter and master thief, far more skilled and dangerous than a mere burglar. However, there was no bigger influence than the vigilante known as the Batman. Inspired by the power that his costume gave him, Selina developed her own alter ego: Catwoman.
As Catwoman, Selina spent years stealing from the rich and corrupt of Gotham City. Despite being a criminal, she had her own code of honor and wasn't above helping those in need. She even assisted Batman and his allies on occasion, though she almost always found a way to profit from it. She drifted away from Gotham City from time to time, including relocating to New York to run for mayor (no, really) after most of Gotham had been leveled in a massive earthquake. However, she always ended up returning to her hometown, seeing it as an integral part of who she was.
Eventually, she reinvented herself as the protector of the East End, donning a practical new costume and standing up for those who the cops didn't care about and Batman didn't have time for. Things were good for a while. She had a small circle of friends and allies. Batman even revealed his identity as Bruce Wayne to her, and the two began an on-again off-again relationship.
Unfortunately, Catwoman's activities led her to cross paths with sadistic crime boss Black Mask. Looking to improve his rep, he targeted and viciously tortured her family and friends. Having learned that her heroic actions were possibly nothing more than the mental manipulations of Zatanna, Catwoman quite literally went gunning for Black Mask, shooting him point-blank in the face to protect her people.
Shortly after this, Selina ended up with a daughter, Helena by a totally useless character who was quickly killed off. And he was also the son of a previous fling. Ew. The mantle of Catwoman was passed onto Selina's longtime friend Holly Robinson for a while. Unfortunately, Selina had made a lot of enemies over the years, from gimmicky villains to super-powered communists. After three separate attempts on Helena's life, Selina had Bruce arrange a blind adoption to prevent her from ever being linked to Catwoman again.
Catwoman has been edging back into villain territory, but growing closer to Batman as well. While she'll still protect the innocent and help the good guys, she's also more vicious and unpredictable than ever.