Mathilde Jacob (8 March 1873 – 14 April 1943) was a German typist and translator who during the First World War became politically involved, working with the anti-war Spartacus League and as a founder member of the German Communist Party. She came to politics through her work for Rosa Luxemburg whose friend and close confidant she became. Although Mathilde Jacob continued to be politically engaged in the 1920s, her greater contribution to history comes from her having smuggled Luxemburg's letters and documents out of Luxemburg's prison cell during her friend's various incarcerations during the 1914–1918 war. She then preserved much of Luxemburg's written legacy after the latter's murder.
By the time the Nazis took power early in 1933 Mathilde Jacob had for most purposes retired into obscurity, but her personal history of communist activism and her Jewishness nevertheless made her vulnerable. It is thought that she attempted to escape from Germany in 1936 but without success. In 1939 she did succeed in transferring some of the letters written to and by Rosa Luxemburg to the United States. She died in the Theresienstadt concentration camp, having been arrested and deported at the end of July 1942. Following Jacobs' death, the authorities attending to her confiscated assets recorded a claim from her landlord that she was liable to pay for some repairs on her apartment, also noting that rent on the property had not been received for three months.
Mathilde Jacob was born in Berlin. She was the eldest child of Julius and Emilie Jacob who ran a small meat wholesale business. In 1907 she set herself up as a freelance typist and translator in the Berlin-Moabit quarter. In her little agency she at times employed an assistant, and at one stage she took on a trainee. Clients for whom she typed up manuscripts included the political radicals Julian Marchlewski, Franz Mehring and, from 1913, the influential philosopher Rosa Luxemburg. Jacob was deeply impressed by Luxemburg, and became supportive of the anti-militarist campaign in which Luxemburg was engaged. She is described in sources as having become Luxemburg's reliable confidant, and in practical terms was able to be particularly helpful during Luxemburg's various periods in prison, looking after her friend's apartment and attending to Mimi, the cat, who died while Luxemburg was away in prison. It is also clear that Luxemburg, who had not been convicted but for much or all of this time was simply being detained in "protective custody" was able to receive visitors and was not prevented from writing copiously while she was in prison. Jacob was able to smuggle several important manuscripts out of the jail, including the "Spartacus letters" ("news sheets") and the "Junius" pamphlet, Luxemburg's important critique of the crisis unfolding in the Social Democratic Party, in the wake of the party leadership's decision to agree what amounted to a parliamentary truce, notably on matters involving funding for the war, for its duration. However, although the Junius pamphlet subsequently became something of an iconic document, at the time it proved impossible to find a publisher for it till after Luxemburg's (temporary) release from prison in 1916. From 1917 Mathilde Jacobs also worked intensively with Luxemburg's political associate Leo Jogiches: their collaboration lasted well into the revolutionary period that Germany experienced directly after the war. Jacobs was certainly present at the three day party congress that started on 30 December 1918 which marked the foundation of the Communist Party of Germany. It is likely that she participated actively in it.