Karl Giese (18 October 1898 – March 1938) was a German archivist, museum curator, and the life partner of Magnus Hirschfeld.

During this time, Giese met the British archaeologist Francis Turville-Petre and the French author and later Nobel Prize laureate André Gide.

Karl still referred to Hirschfeld as "Papa".Ellen Bækgaard, a dentist from Copenhagen and World League for Sexual Reform committee member, describes Giese in her memoirs as the "woman of the house".

He also made contact with the magazine Nový Hlas: List pro sexuální reformu (New Voice: Journal of Sexual Reform), arranging the publication of some articles by both Hirschfeld and himself.

Hirschfeld and other benefactors (Bækgaard and Norman Haire) covered his living expenses and expected him to take up the study of medicine in London after completing exams in Vienna.

Two months before his death, Hirschfeld had designated Li Shiu Tong and Karl Giese as his principal heirs, stipulating in his will that both men should use their inheritances to advance sexual science, not for personal expenses.

[7] It is known that around this time he was still in contact with the two transgender pioneers, the Jewish German-American actress Charlotte Charlaque and the German painter Toni Ebel, whom he knew from Berlin and who, like Giese, had fled to Czechoslovakia after 1933.