Otto Fritz Harder (Nickname: Tull Harder; born 25 November 1892 in Braunschweig, died 4 March 1956 in Hamburg) was a Footballer for Eintracht Braunschweig, Hamburger SV, and Victoria Hamburg.
He won two German football championships and played 15 times in the German national team.
Harder was a former SS officer and had been a warder at the Ahlem concentration camp in Hanover.