Maren Margrethe Thomsen, known as Maren Margrethe "Grethe" Bartram and "Thora" (23 February 1924 – January 2017), was a Danish woman who informed on at least 53 people from the Danish resistance movement during the Second World War, resulting in the early communist resistance groups being dismantled and many of their members being sent to Nazi concentration camps. Bartram informed on her brother, husband and close acquaintances.