The Cheka (Russian: Всероссийская чрезвычайная комиссия по борьбе с контрреволюцией и саботажем (The All-Russian Extraordinary Commission for Combating Counter-Revolution and Sabotage), abbreviated ЧК or cheka) was an organization formed in December 1917.
The Cheka was known for torturing its victims and it is estimated that as many as 500,000 people were murdered by this group.
In 1922 the Cheka was integrated with the NKVD.
Riasanovsky, Nicholas V. A History of Russia. Oxford: University Press, 2005.