Friedrich Nietzsche died in August 1900 (not before suffering a mental collapse). His sister was Elisabeth Forster-Nietzsche.
After his death, she took it upon herself to publish some of his work which is known as The Will to Power. She also took it upon herself to alter his writing to be more in line with her own views. She was a member of the Nazi German Party (her brother was not).
After this, some believed that Friedrich Nietzsche was a Nazi sympathizer, yet his unaltered work does not show this to be true.