Answer
Sidney Reilly was an English-born adventurer, spy and secret agent who vanished in mysterious circumstances in Soviet Russia in 1925. It is believed that he was captured by the Soviet Cheka and executed during the Cheka's Operation Trust, a secret counter-intelligence operation designed to lure British agents into the Soviet Union. Reilly's disappearance has been the subject of much speculation and conspiracy theories, and his body has never been found.