Joseph Stalin
When the provisional government cracked down on Pravda, Stalin protected Vladimir Lenin (the editor at the time), moving him between safe houses in Petrograd and then eventually to Razliv. Stalin remained and acted as leader of the Bolsheviks in Lenin's absence.
Eventually, Stalin and others directed the Octobor Revolution, consolidating power for themselves. Stalin become one of four leading the government alongside Lenin.
After Lenin died, Stalin outmaneuvered his rivals to control the party and would become infamous for his brutal dictatorial rule (1929-1953) during which millions of his own citizens died.
Vladimr Lenin
Lenin pushed for an armed uprising in Petrograd in 1917 where the government clashed violently with the demonstrators. Throughout 1917, Lenin would come and go from Petrograd, at times fearing for his life, but all the while continuing to agitate and plan the overthrow of the Provisional Government.
In October, Lenin's Bolsheviks besieged the government (October Suprise) and Lenin became Chairman of the new Council of People's Commissars and the first head (1917-24) of the Soviet state.
Grigory Zindviev
While Zinoviev and Lenin shared the same end goal, Zinoviev disagreed with Lenin on one major point -- Zinoviev opposed the use of force. Pressure from within the Central Committee eventually let Zinoviev and others to resign, leading Lenin to declare Zinoviev a "deserter." Eventually, Zinoviev regained his favor, and as an outstanding orator helped win public support for the new Communist regime.
In the years to follow, Zinoviev became a central figure in the Communist Party leadership in the Soviet Union. He later was a victim of Joseph Stalin’s Great Purge, even though Stalin and Zinoviev had been close political allies for a time.
Lavr Kornilov
When the February Revolution of 1917 transpired Kornilov was assigned military control of Petrograd (St. Petersburg) where he attempted to restore cohesion in a deteriorating Russian Army. Kornilov didn't remain in Petrograd for long, resigned and returned to the front.
In August, Kornilov was promoted to commander in chief by newly appointed Prime Minister Alexander Kerensky. The two had widely differing political views and their distrust of one another came to a head when Kerensky sent troops toward Petrograd in an apparent coup attempt (Kornilov Affair), which Kerensky promptly quashed by dismissing Kornilov and barring his troops from rail access.
In September, Kornilov was arrested and imprisoned. He soon escaped and would lead an anti-Bolshevik army until his death a few months later.
Alexander Kernesky
In May 1917, Kerensky became Minister of War but was criticized for an unsuccessful military operation during WWI. His blundered offensive was quickly overshadowed by the Bolshevik uprising in July. It was then that Kerensky succeeded Prince Lvov as Russia's Prime Minister.
By October 1917, Kerensky's government had lost nearly all support and the Bolsheviks seized control. Kerensky fled to France and later emigrated to the United States at the start of WWII.
Georgy Lvov
As leader of the Union of Zemstvos during WWI, Lvov provided relief for the sick and wounded and procured supplies for the army, winning the respect of many politicians and army commanders.
When Emperor Nicholas II abdicated the throne in 1917, Lvov became the first head of the Russian provisional government.
Unable to satisfy the radical demands of an increasingly volatile public, Lvov resigned his position after a few short months and was replaced by his Minister of War, Alexander Kerensky.