 Complete the following phrase:  Yakov Saulovich Agranov  born Yankel Samuilovich Sorenson; 1893  1938 was the first chief of Soviet Main Directorate of State Security and a deputy of NKVD chief Genrikh Yagoda. He is known as one of main organizers of Soviet political repressions and Stalinist show trials in 1920s and 1930s. He fabricated the Tagantsev conspiracy case and Moscow trials, including Trial of the Twenty One and 