Russia's highest scoring ace was educated in military schools and entered the army in 1908. After serving in the cavalry, he transferred to aviation in 1913 and by the following year was assigned to the 4th Corps Air Detachment in Poland where he flew reconnaissance and bombing missions in a Morane-Saulnier. Having made several unsuccessful attempts to bring down enemy aircraft by dangling explosives and grappling hooks beneath his plane, Kozakov scored his first victory in the spring of 1915 by ramming his opponent.

In September of 1915, he assumed command of the 19th Corps Air Detachment but scored no additional victories that year and only 2 more by August of 1916 when he assumed command of the 1st Combat Air Group. In February of 1917, his CAG was ordered to Romania where Kozakov scored eight more victories before being wounded in action on 27 June 1917. With 20 victories, he resigned his commission in January of 1918 and joined the British Joint Military forces at Murmansk in June. Promoted to the rank of Major, he commanded the Slavo-British air detachment at Benezniky and continued flying combat missions until he was again wounded in January of 1919

In March, he returned to duty but became deeply depressed by the withdrawal of British forces from Russia in the summer of 1919. On the evening of August 1, 1919, ignoring an invitation to a farewell dinner for British pilots, he took off in a Sopwith only to crash to his death a few moments later. Having watched Kozakov pull a loop at low altitude and stall the plane,Ira Jones concluded the Russian Ace of Aces "brought about his own death and staged it in the most dramatic manner."