Communism in general is very revolutionary, but as to Lenin, he was revolutionary because he changed a capitalist society to a communist one and began the Soviet Union which would become a great success until Stalin.
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One of the biggest factors in Lenin's lifetime was his relationship with his executed older brother. From a young age, Vladimir had grown to admire his brother and read the same books he had read (which turned out to be books such as What Is To Be Done by Nikolai Chervyshevsky). Fueled by anger when his brother was executed for attempted assassination on Czar Nicholas II, Lenin began reading what his brother read in more depth. From that, he began to understand what his brother was aiming for and began intrigued by the idea of a workers' rebellion. Karl Marx's books, such as the famous The Communist Manifesto, inspired Lenin too. Soon, he began to understand a proletariat rule. Both his anger at the Czar and the execution of his brother allowed Vladimir Lenin to develop an admiration for communism.
The story of Stalin's rise to General Secretary of the USSR/Dictator is complex. I have added a link for you to read.