Abigail Marjorie Lockhart, M.D. (née Wyczenski) is a fictional character from the NBC medical drama series ER, portrayed by Maura Tierney. Usually referred to as simply Abby, she first appears as a guest star in the first half of the sixth season, before becoming a main character later that season, appearing until the beginning of the fifteenth season. Tierney returned to make one final guest appearance later in season fifteen.
