Berek Lajcher (24 October 1893 – 2 August 1943)[1] was a Jewish physician and social activist from Wyszków before the Holocaust in Poland, remembered for his leadership in the prisoner uprising at Treblinka extermination camp.

After the German invasion of Poland during World War II, Lajcher was expelled by the Nazis along with all Polish Jews from Wyszków, and relocated to Węgrów, from where he was deported to Treblinka, the secret forest camp where Jewish men, women and children were being murdered in gas chambers.

On 2 August 1943, after a long period of preparation, the prisoners stole some weapons from the arsenal and made an attempt at an armed escape from the Totenlager.

[1] At the very beginning of World War II, all Polish Jews of Wyszków, including Lajchers' family, were expelled by the Nazis in one massive action of 4 September 1939.

[1] The extermination of Jews by semi-industrial means throughout the country began in early 1942 and continued until all Jewish ghettos in German-occupied Poland were liquidated.

Following the liquidation of the small ghetto in Wegrów on 26–27 April 1943, during which his wife and 13-year-old son were murdered, Lajcher was brought to Treblinka in a Holocaust train on 1 May 1943.

[13] The Organizing Committee at Treblinka Totenlager included Zelomir Bloch (leadership),[14] Rudolf Masaryk, Marceli Galewski, Samuel Rajzman, Dr. Irena Lewkowska (sick bay),[15] Leon Haberman, and several others.

[17] Lajcher launched the uprising on a hot summer day when a group of Germans and Ukrainians drove off to the Bug River for a swim.

[4][13] On 2 August 1943 (Monday, a day of rest from gassing), the heavy door to the Nazi "arsenal" near the train tracks was silently unlocked by the Jews and some 20 rifles, 20 hand grenades and several pistols were stolen in a cart.

[18] Only about 70 Jews are known to have survived until the end of the war,[19] including future authors of published Treblinka memoirs: Jankiel Wiernik, Chil Rajchman, Richard Glazar, and Samuel Willenberg.