Osman Musayevich Kasayev (Russian: Осман Мусаевич Касаев; 11 October 1916 – 18 February 1944) was a Karachay Major in the Soviet Army during World War II who commanded a partisan detachment after his artillery division was defeated by the Germans during Operation Barbarossa.

His detachment eventually became the 121st Partisan Regiment, and under his command the unit was credited with resulting the deaths of over 1,000 German soldiers before he died of injuries from an airstrike in 1944.

In the late August of 1941, upon reaching Byalynichy district of Mogilev region, Byelorussian SSR, a group of fighters and commanders, including Kasayev, decided to start combat operations as partisans.

Detachment was successfully fighting in Mogilev region, destroying garrisons, punitive units, warehouses, motor depots, and headquarters.

On 17 February of 1944, during the transition between settlements in Byerazino district (Minsk region, BSSR) the partisan column was attacked by the German air force.