Piper Halliwell is an alternate universe version of her heroic counterpart from the main Charmed universe.
She is a witch who is a part of the Evil Charmed Ones. She was presumably the daughter of this world's Victor Bennett and an evil witch, Patricia Halliwell. She's the half sister of Paige and the sister of Phoebe and Prue Halliwell. She's also the wife of the darklighter, Leo Wyatt, the mother of Wyatt and Chris Halliwell (whom she was pregnant with at the time) and eventually went into labor with Chris when Gideon tried to kill her son Wyatt. Little is known about her except she's got a legendary temper.