Therese Elisabeth Alexandra Förster-Nietzsche (July 10, 1846 – November 8, 1935), who went by her second name, was the sister of philosopher Friedrich Nietzsche and the creator of the Nietzsche Archive in 1894.
Förster-Nietzsche was two years younger than her brother. Their father was a Lutheran pastor in the German village of Röcken bei Lützen. The two children were close during their childhood and early adult years. However, they grew apart in 1885 when Elisabeth married Bernhard Förster, a former high school teacher who had become a prominent German nationalist and antisemite—Friedrich Nietzsche despised antisemitism.See e.g. Nietzsche, Nice, end of December 1887: Draft of letter to Elisabeth Förster-Nietzsche:
In the meantime I've seen proof, black on white, that Herr Dr. Förster has not yet severed his connection with the anti-Semitic movement. [...] Since then I've had difficulty coming up with any of the tenderness and protectiveness I've so long felt toward you. The separation between us is thereby decided in really the most absurd way. Have you grasped nothing of the reason why I am in the world? [...] Now it has gone so far that I have to defend myself hand and foot against people who confuse me with these anti-Semitic canaille; after my own sister, my former sister, and after Widemann more recently have given the impetus to this most dire of all confusions. After I read the name Zarathustra in the anti-Semitic Correspondence my forbearance came to an end. I am now in a position of emergency defense against your spouse's Party. These accursed anti-Semite deformities shall not sully my ideal!! Nice, end of December 1887: Draft of letter to Elisabeth Förster-Nietzsche

As his caretaker, Förster-Nietzsche assumed the roles of curator and editor of Nietzsche's manuscripts. She reworked his unpublished writings to fit her own ideology, often in ways contrary to her brother's stated opinions, which were strongly and explicitly opposed to antisemitism and nationalism. Through Förster-Nietzsche's editions, Nietzsche's name became associated with German militarism and Nazism, although later 20th-century scholars have counteracted this conception of his ideas.