Ivan Alexeyevich Polyakov (Russian: Ива́н Алексе́евич Поляко́в; 1886-1969) was a Cossack military leader who fought in World War I (on the Russian side), and in World War II (on the German side).
According to his file at the Hoover Institution website, he joined Pyotr Krasnov's Cossack army in 1917.
In World War II he joined Andrey Vlasov's Russian Liberation Army (ROA), which fought on the side of Germany against the Soviet Union.
[1] In 1949 a letter of his was published in the journal Russia, describing the post-war fate of the Cossacks who had fought on the German side against the Soviet Union.
He claimed that tens of thousands were killed by the Red Army after being violently repatriated by British troops.