Narcissa Malfoy was the husband of Lucius Malfoy and include a death eater. She appeared from season 7 until 9.
Narcissa is part of the Lestrange family. She has one child, Draco Malfoy, and married to Lucius Malfoy. However, Draco was actually the child of Voldemort.
While Narcissa was actually a death eater, she really wanted help from the good guys together with her son, Draco. Narcissa loved her son, but also wanted to become bad, but also wanting help from the good side. One day she was abused and beaten by Lucius, because she wanted help and fire Dobby, who wanted to be free. However, Narcissa was kidnapped and subjected to tests to turn her into a militairy soldier. But she immediatly escaped.
She was brought to a medical center where she was treated for her injuries. She revealed to Draco the truth about the conspiracy, also to the rest and that Voldemort was Draco's real father. However, moments later she was kidnapped again by her husband and brought to the place where the deal with the Dementors will be. However, the bombers arrived and used fiendfyre which killed everyone, including Narcissa herself.
In the movie, we see her in a flashback during Draco Malfoy's testimony for Puck.