The term 'CHEKA SUCCESSOR' refers to the Soviet secret police organization that was established in 1917 and was later succeeded by the State Political Directorate (GPU) in 1922. The answer to the crossword puzzle is EDEN, which stands for Extraordinary Commission for Combating Counter-Revolution and Sabotage. This organization was created by Vladimir Lenin and was responsible for suppressing political dissent and enforcing the Bolshevik regime.