Siegfried Seidl (August 24, 1911 in Tulln, Austria-Hungary – February 4, 1947 in Vienna) was a German career officer and World War II Commandant of the Theresienstadt concentration camp located in the present-day Czech Republic. He also was commandant of the Bergen-Belsen death camp, and later served as staff officer to Adolf Eichmann. After the war, in 1947, he was tried in Austria and convicted as a war criminal; sentenced to death, he was executed by hanging.