Stalin's goal was to have absolute personal power over the Soviet Union. He changed his name to Stalin, meaning man of steel, as a hint to his personality and the way he would achieve his goals.

Early on in the Russian Revolution, Stalin pursued power, building a broad base of support by joining every possible committee. He put his own desire for power ahead of the best interests of the Soviet Union, for instance, by driving out the dedicated and highly intelligent true believer, Leon Trotsky. Once he had power, he consolidated it ruthlessly, murdering anyone he remotely conceived might possibly be a rival or enemy. He also conducted purges of the Russian people, executing those considered enemies of the state. Whether or not they were enemies mattered less than spreading terror and convincing everyone that all that mattered was absolute loyalty to him. He was quite willing, for example, to execute people with expertise if they appeared to challenge him and replace them with incompetent but loyal followers.

Besides elevating himself as a near-mythic figure of absolute power, Stalin used his power to institute his vision of the socialist state. He wanted the Soviet Union to be the supreme world power and to spread communism across the globe. He was insistent that the USSR, a country lagging economically at the time of the revolution, quickly become a major industrial power, no matter what the cost. He also wanted to collectivize farming both to bring it under state control and make it more efficient. He was willing to go to any lengths to achieve these goals, stating that "one death is a tragedy; a million deaths are a statistic."

While Stalin was a ruthless tyrant in the mold of Adolf Hitler, he had learned the lessons of how past attempts at revolution had failed because the displaced ruling classes quickly turned ruthless once they were given any bit of power in a coalition regime. He was also the right man for opposing Hitler's attempt to crush the USSR, as one thing Stalin would never do would be to give up power. His ruthless determination to industrialize the country also served it well during World War II, as the Soviets were able to churn out war materials at a pace that the Germans were unable to match. Nevertheless, Stalin is not the leader that most countries would aspire to have.

One of Stalin's main goals was to expand the Soviet Union's political power and influence, both geographically and politically. Motivated by rapidly developing Western societies and the expansion of capitalism, Stalin's aim was to ensure the Soviet Union's stability and safety by establishing it as a great economic, militaristic, and sociopolitical power. As a communist, nationalist, and patriot, Stalin also intended to promote communism and the communist worldview to help spread the ideology on a global scale. Mainly, he wanted the USSR to be a global superpower.

Personally, Stalin wanted to become an established name in world politics, and so his thirst for power and his desire to industrialize the Soviet Union were essentially his main motives.

It's notable to mention that Stalin did, in fact, manage to achieve some of his goals, albeit with questionable methods. He took control of the USSR's economy and politics and transformed the Soviet Union from an agricultural society into an industrial and modern world power. After becoming the ruler of the Soviet Union in 1927 and the premier of the Soviet Union in 1941, Stalin was officially recognized by the Western societies as a powerful and influential political figure. He remained in power and lead the USSR until his death in 1953.

As pohnpei remarks, Stalin had a personal goal to gain as much power as he could for himself at the apex of society in the Soviet Union, and to maintain that power. He was ruthless in dealing with enemies, real and imagined, leading to the creation of a society where people were afraid to challenge him. He was liable even to turn on those that might appear closest to him in the centre of power in the Communist Party. His motivation for this undoubtedly sprang from his personal ruthless temperament - a temperament that had been further hardened during the days of absolute turmoil, hardship and civil war that surrounded the Communist Revolution in Russia in 1917.

However, this remorseless concern with absolute power (while attempting to maintain something of the facade of an open, free society) also came from the fact that, having achieved control in such turbulent circumstances, Stalin was determined that the Communist Party should retain the leadership of the country at all costs. In addition, Stalin and other tough, ruthless men at the top of Party hierarchy felt it was imperative to maintain absolute control during the drive to modernize the Soviet Union. Russia had long been a technologically backward country but Stalin's broader goal was to make his country an advanced, modern society capable of challenging Western powers, as pohnpei observed. To achieve modernization in a relatively short time was an enormous task, and Stalin evidently felt that it could only be achieved in a ruthless manner. Witness, for example, his treatment of the more wealthy peasants (kulaks) who did not want to be part of his vast collectivization schemes, and were brutally coerced. 

Stalin, then, had the personal goal of achieving and keeping power for himself, and the broader aim of modernizing his country as fast as possible. In this last aim, he was certainly motivated by the urgency of keeping pace with the Western powers in an uncertain time of economic crises and world wars. However, contrary to what pohnpei suggests, he did not necessarily envision the spreading of Communism across the globe. This was certainly what the likes of Lenin and Trotsky had wanted earlier, but Stalin came to see that it was not a realistic aim and settled on the principle of 'Socialism in One Country'. If the Soviet Union was going to be isolated as a Communist country, he would make sure it was strong enough to take its place as a world power and defend itself against other nations.

Joseph Stalin had two major goals, one personal and one related to his country and ideology.

On the national/ideological level goal, Stalin wanted to create a Soviet Union that was strong enough to challenge the West.  His motivation was that he wanted a country that would be able to help spread communism across the world.  This country would, ideally, be both an economic and a military power.

On the personal level goal, Stalin wanted power.  He wanted to be the one person in control of the Soviet Union.  This can be seen very clearly in the bloody purges that he ordered.  The main goal of these purges camefrom his motivation to ensure that no one in the Soviet Union would have any chance of taking power away from Stalin.