Stalin was born on December 18th, 1878 to a cobbler and his family, in Gori Georgia. In his early life, Stalin seemed set on joining the ministry, and attended a theological school. However, he was expelled, most likely due to his failure to pay tuition.
After leaving Seminary, Stalin joined up with the Bolshevik movement in the Caucus, and became one of their most prominent and active members. He helped finance party operations with bank robberies and ransomed kidnappings. He was arrested on multiple occasions and sent into exile multiple times.
Upon returning from one exile, he became editor of the St Petersburg Pravda, a position formerly held by Leon Trotsky, which marked a close connection to revolutionary leadership. It was this appointment which secured that he would be involved with the Soviet Command; for if he had not, he would have likely never gotten the chance to meet Lenin.
With his position of power at the Pravda, he helped secure the safe-being of Lenin when counter-revolutionaries tried to imprison him. By this time, the Bolshevik congress had voted in favor of insurrection against Aleksandr Kerensky's provisional government. Stalin was with Trotsky and Lenin during the height of the activities of the October Revolution, to include the storming of the winter palace.
After the October Revolution, Russia broke apart into a civil war. On one side you had the rebellious elements of the Red Army, and on the other side you had the many disparaging forces of the White Army (supported by internationalist forces). Stalin was appointed as military commissioner of the city of Tsaritsyn, where he was responsible for keeping good order, and maintaining supply routes to Red Army forces.
In this task he excelled, and he was known for very stark and brutal actions to keep the War Effort going. He was known to execute former White Army Officers, deserters from the Red Army, and he even burned villages to force the peasantry into submission.
After the war was ended, he found himself the counter force to everything Trotsky suggested. Even going so far as to oppose Trotsky's ideas on how to fight the early war with Poland, in doing so, he lost the War for the Soviets, and sentenced the Western Revolution in Germany to failure. Naturally, this created a power vacuum for Hitler to step into.
Stalin's Rise to Power
Lenin, seeing a disparaging future for the Soviet Union, decided, with the help of Lev Kamenev, to appoint Stalin as General Secretary of the Communist Party. Stalin had shown great promise in the invasion of the Georgian Socialist State(which Stalin had moved to make happen), though his following repression was a foreshadow of what was to come. However, Lenin had a stroke, and had to retire, and Stalin became one of his few lifelines to the world.
As Lenin's condition deteriorated, so to did his opinion of Stalin. He came to dislike his politics, his personality, and the manner with which he ruthlessly sought his goals. He penned, in his last testament, that Stalin shouldn't be General Secretary. However, Lev Kamenev decided to keep this testament a secret, and Stalin became Lenin's successor.
As Stalin solidified his power base, Trotsky was exiled from the Soviet Union, and later killed on Stalin's orders. With this, there was none left to challenge his right to rule.
The Red Purge & the 30s
Just as Hitler had escalated control of Nazi Germany through the Night of Long Knives, Stalin had his own purge. He utilized a secret police force (the NKVD) to carry out his cleansing of the Soviet Upper Echelon, and end all opposition to his own power. In this decade, we can easily see the transformation from a Socialist State that utilized Totalitarianism, to a Totalitarian State that utilized Socialism.
This can also be seen in Stalin's redaction of Lenin's New Economic Policy. This would solidify power into his hands, but alienate the vast majority of small business owners and the middle-class. However, this would allow him the power and capability to ramp up industrialization, in order to build Soviet Weapons of War and Vehicles for the coming conflict.
The Great Patriotic War, and Death
Stalin was General Secretary of the CCCP during the start of the war, and ultimately, the leader of the broader socialist empire. His policies of industrialization would help the Soviets survive the Operation Barbarossa(link forthcoming), and his policies would be seen in every part of the Eastern Front.
Following the end of the 2nd World War, Soviet forces were now locked in a cold war with the Western Nations. A nuclear arms race and a race to space would dominate, as these two powers competed around the world for political support, viable markets, and in direct conflict. However, Stalin wouldn't long see what he had built as he died from a stroke (though some suggest it was poison) on March 5th, 1953.