6. Sidney Reilly
Sidney Reilly was a master spy as he worked for several governments at the same time. He was said to be a master of disguise and shared good rapport with the wives of military officers and politicians. He stole information related to aircraft prototypes, military secrets and building plans. He was known to cross borders assuming different identities making it impossible for the authorities to capture him. He was however, arrested in 1925 and executed by the firing squad.