Angelika (Geli) Raubal, was the daughter of Adolf Hitler's half sister, Angela Raubal. As Adolf grew to power in Germany during the late 1920s, he became infatuated with his niece Geli and carried on what some felt was a borderline sadomasochistic affair with her.
Geli was not well received by the higher ups in the fledgling NAZI party, particularly Goebbels, nor was she friendly with Eva Braun, whom she most certainly saw as a rival.
In 1931, she was found dead in Hitler's apartment with a gun in her hand and a suicide note on the desk. Most believe that she killed herself, but it's possible, and some evidence suggests that, she was murdered by Hitler, although he did still claim that she was the only woman he ever loved.
In 1999, Ron Hansen, author of Atticus, penned a novelization of these events in a book entitled Hitler's Niece.