Stalin was more calculating than Lenin or Trotsky and didn't wear his beliefs on his sleeve. To a certain extent, he had a superstitious fear of religion that Lenin and Trotsky didn't, which is evident from his relationship with the Orthodox Church and probably due to his education in the Tiflis (Tbilisi) Religious Seminary.

[brief aside: Stalin authorized vicious anti-religious campaigns in the 1930s, but when the Nazis invaded, he found some fear in God and summoned Orthodox religious leaders to the Kremlin. They told him that he should allow the Church to hold religious processions around Moscow, Leningrad and Stalingrad in order to bless the nation. He permitted these processions and allowed the churches to reopen in many places. After the war and until his death in 1953 there were no further persecutions of the Orthodox Church. Persecution began again only under Khrushchev]

However, the idea that he was just a thug betrays a poor understanding of his personality (and it is repeated by many historians, even in Russia). We know that he was reasonably well educated and could not finish the Seminary because his family was too poor. However, the grades that they show were as follows: Holy Scripture - A (5 in the Russian system), Ancient Greek - B (4), Choir - A (5), Grammar - A (5), History - A (5), Mathematics - A (5), Georgian Language - A (5), Composition - B (4).

the fact that he received only a "B" (4 in the Russian system) in Ancient Greek is not a sign that he was stupid. The very fact that he had to know Greek and Church Slavonic in addition to Russian and his native Georgian is a rarity.

Perhaps the school was not very rigorous. However, it is worth noting that these grades were given in the late 19th Century, when grade inflation was a relatively unknown phenomenon. Furthermore, we know that Stalin, as a young man, wrote poetry in Georgian. I only know a few words and phrases in the language and can't assess the quality of his poetry independently, but people whom I know who speak Georgian speak quite highly of the aesthetic quality of his poetry.

The "thug" reputation seems to stem from (a) the fact Stalin was Georgian and (b) the armed robberies he committed in the name of revolution. The latter speak for themselves, but the former requires a bit of explanation. All nationalities are characterized by stereotypes, which are generally valid or invalid in varying degrees. Georgians, like most of the peoples of the Caucasus, have a reputation that is similar to the reputation of many Mediterranean peoples. They are passionate and hot-tempered, loving wine, singing, generous gifts and hospitality, long toasts at celebrations which last for days and are filled with an overabundance of food and drink, and blood feuds that run deep. As one friend said of his Chechen acquaintances, "He could have that same warm smile on his face as he slits my throat if he ever gets it into his head that I've betrayed him in some way." The same has been said of Georgians.

Stalin in many ways lived up to that reputation. If you want to see what his day-to-day life was like, read Milovan Djilas's "Conversations with Stalin". It's a fascinating book by the Yugoslav communist turned dissident who spent years as the official emissary of Tito to the Kremlin. Stalin was always warm and hospitable, made sure that every evening there was a giant feast, everyone would drink, and then he would start with his paranoia. The distrust ran very deep.

At the same time, Stalin's actions show a very keen interest in continuing the ideological principles of the Revolution. Had Stalin only been interested in power, he didn't need to engage in social upheaval on a massive scale to achieve it. The New Economic Policy (NEP) that Lenin had started as a concession to capitalism was working more or less fine. Russia would have looked like 1980s China, in effect, and Stalin could have just used his popularity to stay in power. He could have delivered comforts to his people and made the Soviet Union the envy of the world (at least in the 1930s, when the economic isolation of the USSR and centralized economy shielded it from the Great Depression).

Instead, he launched devastating campaigns of collectivization, state-run industrialization and militarization on a scale never seen before or since anywhere in the world.

[Aside: China's collectivization was never fully completed and began to be reversed in the early 1980s under Deng Xiaoping. Its industrialization was largely through joint ventures and direct foreign investment rather than state-run. And no nation militarized the way the USSR did in the 1920s and 1930s]

People starved so that Stalin could buy equipment needed for his massive industrialization projects. And those projects weren't to benefit people. They were to build tanks, planes and artillery. When the Nazis invaded the Soviet Union, they had something like 6,000 tanks involved in Barbarossa. The Red Army had 30,000 tanks, most of them of superior construction (as evidenced by the fact the Nazis painted a military cross on many and used them against the Soviets). The Red Army had the largest air force in the world.

The Soviet Union was not building this massive arsenal for decades in order to defend itself.

Stalin publicly stated that the USSR's policy was to build socialism in one country, but in private statements and in a wealth of documents that are now public or were at one point made public to historians it is clear that he never disavowed the fundamental principles of Lenin, that the revolution must be carried throughout the world.

Stalin did not see the victory over Nazi Germany as a victory for this reason. At Potsdam, when Truman said, "You must be very happy to have taken Berlin," Stalin sourly replied, "Tsar Alexander got to Paris." This was why Stalin refused to be the "accepting side" in the victory parade, instead letting Marshal Zhukov accept, on behalf of the nation, Marshal Rokossovsky's report of the defeat of Germany. Ceremonial mattered to Stalin.

Everything that he did was to prepare for the export of the Revolution. He blew up the Cathedral of Christ the Savior on the Moscow River in 1934, just next to the Kremlin, in order to build a Palace of Soviets. The building was to be taller than the Empire State Building, with a statue of Lenin taller than the Statue of Liberty on the top, whose outstretched hand would follow the sun across the sky by means of a rotating base.

The plans for the Palace betray the full scope of Stalin's plans. There are halls for the Spanish Soviet Republic, the Chinese Soviet Republic, the Mexican Soviet Republic, and even the American Soviet Republic. It was to be the building from which the entire world was governed.

The foundation was laid at great expense but the building was never built because the steel was needed for the war effort. After the war the site was repurposed as a massive outdoor heated pool, which operated even in winter. After the fall of the Soviet Union the cathedral was rebuilt exactly as it had been up to 1934.

At the time of the Nazi invasion, the Soviets were massing their forces at the Western border and in the process of finishing their mobilization (full combat readiness was to be achieved July 6, 1941). The stunning success of the Wehrmacht was in part due to the fact that they caught the Soviets in the middle of their mobilization, with hundreds of thousands of soldiers in transit on trains, thousands of planes lined up right by the border on the ground and vehicle parks filled with empty tanks. Historians argue about whether or not Stalin was really going to attack Germany in 1941, but no one disputes the consensus that Stalin was preparing to attack Germany by 1942 at the latest. Stalin's refusal to listen to reports that the Germans were getting ready to attack make sense in this light - Stalin saw no evidence that the Germans had prepared cold-weather fuel for tanks, or winter boots or coats for their army, and thought the reports were provocations to force his hand before he was ready. It never occurred to him, with his 30,000 tanks, largest air force in the world and largest army in the world, that the Nazis thought they could finish off Russia before winter.

The extent of the Soviet war preparations shocked even Hitler. I have linked, below, the rare recording made of him without his knowledge (where he uses his normal, everyday tone of voice) where he explains to Marshal Mannerheim of Finland, how shocked he was at the Soviet war preparations. It reinforces the extent of Stalin's preparations.

These are the actions of a person who fundamentally committed himself to the Revolution. A revolution he would lead, certainly, but one that he gambled his life and future on by taking massive risks. He was a bright man who wrote competent poetry, but who was filled with paranoia and distrust and therefore worked quietly and in a calculating manner, accomplishing the same goals as Lenin.

As a final aside, Lenin, in his "political testament", accused Stalin of being power hungry but did not criticize his ideological stances the way he criticized those of Trotsky, or Zinoviev, or Kamenev, or the other members of the Central Committee.