Grigory Mikhaylovich Semyonov, or Semenov (Russian: Григо́рий Миха́йлович Семёнов; September 25, 1890 – August 30, 1946), was a Japanese-supported leader of the White movement in Transbaikal and beyond from December 1917 to November 1920, a lieutenant general, and the ataman of Baikal Cossacks (1919).

Commissioned first as a khorunzhiy (cornet or lieutenant), he rose to the rank of yesaul (Cossack captain), distinguished himself in battle against the Germans and the Austro-Hungarians in World War I, and earned the Saint George's Cross for courage.

In July 1917, Semyonov left the Caucasus and was appointed commissar of the Provisional Government in the Baikal region and was responsible for recruiting a regiment of Buryat volunteers.

[5] After the October Revolution of November 1917, Semyonov stirred up a sizable anti-Soviet rebellion but was defeated after several months of fighting, and he fled to the northeastern Chinese city of Harbin.

In January 1918, he invaded Transbaikal, but by February, had been forced by Bolshevik partisans to retreat back to Manzhouli, where he was visited by R.B.Denny, British Military Attache in Beijing, who formed an "extremely favourable impression of him".

[8] The French government also decided to give him financial aid, while the Japanese placed an intelligence officer, Captain Kuroki Chikayochi, in Semyonov's headquarters.

[10] The region under his control, also called Eastern Okraina, extended from Verkhne-Udinsk near Lake Baikal to the Shilka River and the town of Stretensk, to Manzhouli and northeast some distance along the Amur Railway.

In his rule over the Transbaikal, Semyonov has been described as a "plain bandit [who] drew his income from holding up trains and forcing payments, no matter what the nature of the load nor for whose benefit it was being shipped".

[3] In December 1919, Semyonov sent a detachment to Irkutsk, which had been the last city west of Lake Baikal still nominally under Kolchak's rule until a coalition of Mensheviks and Socialist Revolutionaries seized control.

They took their hostages aboard an icebreaker on Lake Baikal, where, on 5 January, they clubbed them to death with a wooden mallet, one by one, and threw them overboard - all except for one man who put up a fight and was thrown alive into the freezing water.

His influence was such that when Anastasy Vonsiatsky of the Russian Fascist Party wanted to visit Manchukuo, the Japanese puppet state in Manchuria, he needed Semyonov's help in getting a visa.

[18] Vonsiatsky, however, saw Semyonov as a threat to his dream of being Russia's Mussolini, and declared that he should be shot, an outburst that led to the Russian Fascist Party splitting in two.