The pioneers of Sambo were Viktor Spiridonov and Vasili Oshchepkov. Oshchepkov died in the prison during the political purges of 1937 after accusations of being a Japanese spy. Oshchepkov spent much of his life living in Japan and training judo under its founder Kano Jigoro. The two men independently developed two different styles, which eventually cross-pollinated and became what is known as Sambo. Compared to Oshchepkov's judo based system, then called "Freestyle Wrestling", Spiridonov's style was softer and less strength dependent. This was in large part due to Spiridonov's injuries sustained during World War I.