Born in Kalisz, Poland, Joseph Kaplan was one of the leaders of Hechalutz and Hashomer Hatzair. At the time of the German invasion,
he escaped to the Soviet zone. Having returned to Warsaw, he became one of the founding members of the Antifascist Bloc, taking command of its military branch. A co-editor of underground publications (partly rediscovered in the Oneg Shabbat Archive), he was an active member of the Jewish Self-Help Committee.
In July 1942, he became one of the leaders
of the Jewish Fighting Organization. Arrested
by the Gestapo on September 3 in the Landau carpentry shop where many of the under- ground activists took refuge, Kaplan was assassinated on September 11th 1942 in Pawiak Prison.
