Arguably, the most prominent and successful Russian general of the First World War. Brusilov's command of the Eighth Army on the Austrian front from 1914 marked him as a cut above most other Russian commanders, but it was not until March 1916 that he was appointed to lead the southwestern army group and had an opportunity to demonstrate his skills on a wider scale.
In planning the offensive of 1916 which bears his name, Brusilov set an example of efficient staff work and preparation unparalleled in the rest of the army. He inspired and enforced loyalty and hard work among his subordinates, countering to a remarkable extent the usually poor coordination practiced by junior Russian commanders. In supply and preparation he also worked miracles, encouraging effective coordination of artillery and infantry. Though not by any means a "soldiers' general," he made a point of frequently visiting the front lines and directing tactics in person, another attribute sorely lacking in the rest of the Russian military leadership.
The two central principles upon which Brusilov based his plan of attack were surprise and dispersion of the enemy's reserves by making several thrusts rather than concentrating his forces at a single point. Despite criticism from his colleagues, he ordered four main attacks on reasonably wide fronts, all the more surprising given that Russian numerical superiority over the Austrian and German forces was minimal - perhaps 132,000 men, with an even smaller edge in artillery. Cavalry had no place in Brusilov's plans for exploitation of breakthroughs.
The Brusilov offensive was launched on June 4, 1916 in Galicia, in rough coordination with Italian and British offensives on the Piave and Somme respectively. Initial Russian successes were tremendous: nearly 200,000 Austrians were taken prisoner in the first week of fighting alone as Russian forces drove deep into Galicia. The Austrian army was effectively destroyed as a major fighting force while Russian advances drove Romania into the Allied camp. Other Russian commanders looked askance at Brusilov's methods however, and their attempts to extend Brusilov's success with traditionally planned and executed attacks further north bogged down almost immediately with heavy casualties. By the time the southern offensive petered out in August therefore, no gains of strategic significance had been made.
Brusilov's contempt for the Tsar and many of his fellow officers is amply expressed in his memoirs, A Soldier's Note-Book. He therefore declined to join the Whites in the ensuing Russian Civil War. Though not a Communist, he joined the Red Army staff in 1920. He died in Moscow.
Sources: Brusilov, General A.A. A Soldier's Note-Book 1914-1918 London: MacMillan, 1930.
Stone, Norman. The Eastern Front 1914-1917. London: Hodder and Stoughton, 1975.
Pope, Stephen and Elizabeth-Anne Wheal, The Dictionary of the First World War New York: St. Martin's Press, 1995.