Abraham Gancwajch

Abraham Gancwajch (1902–1943) was a prominent Nazi collaborator in the Warsaw Ghetto during the World War II occupation of Poland, and a Jewish kingpin of the ghetto underworld. Opinions about his ghetto activities are controversial, though modern research concludes unanimously that he was an informer and collaborator motivated chiefly by personal interest. As a youth, he apprenticed as a journalist and editor in Łódź,

After the German invasion of Poland, he surfaced in Warsaw as a refugee from Łódź, and as a person with connections to the German Sicherheitsdienst (SD). In December 1940 he founded the Group 13 network, a Jewish Nazi collaborationist organization in the Warsaw Ghetto, described by Israel Gutman and Emanuel Ringelblum as the "Jewish Gestapo".

Gancwajch believed the Germans would win the war and called on Warsaw's Jews to serve them as a basic means of surviving. He was also a proponent of the Nazi Madagascar Plan to create an autonomous settlement for all Jews under the protection of the Third Reich in an overseas country. mentioned him in his diary as "a despicable, ugly creature". Janusz Korczak, who ran an orphanage in the Ghetto, when asked why he was dealing with him, replied, "I will see the devil himself to save my children."