Maren Margrethe Thomsen, known as Maren Margrethe "Grethe" Bartram and "Thora" (23 February 1924 – January 2017),[1] 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.

Grethe Bartram was born in Aarhus, and grew up in a poor household, the second of eight children; both her parents were members of the Communist Party of Denmark (DKP), as were the social circles of the family.

Her father, Niels Peter Christopher Bartram (born 1896), was from southern Jutland and participated in World War I on the German side.

He suffered from shellshock from the war and found it difficult to work but managed to operate a small bicycle repair shop in Midtbyen, Aarhus.

[2] Bartram left school at 13 years old and started working until she became pregnant at 16 and was married on 12 July 1941 to a young machinist, Frode Thomsen (born 28 March 1920) from her workplace.

Of those, her information directly resulted in 15 being tortured during interrogation as well as 35 being transported to Nazi concentration camps in Germany, where eight ultimately died or were reported missing.

Busch-Jensen gave as his reasons Bartram's young age at the time, that she had been raised in an "anti-religious, communist and materialistic spirit", and that she had had financial troubles.