Following Putin's annexation of Crimea and the Russian-inspired unrest in Ukraine following the February "revolution", there has been lots of talk of Putin as the "new Hitler". For this reason, it's worthwhile to look at that comparison in more detail, to see how much it stands up to scrutiny.
The "new Hitler" theory
To give this theory a better standing, it also makes sense to compare Nineties Russia with Weimar Germany. To a large extent, this historical comparison rings true.
The effect of the Cold War on Russia/the Soviet Union was politically, socially and economically similar to what the Great War had on Imperial Germany.
After the Great War, Imperial Germany was constitutionally ripped apart (by losing its imperial status and converted to a republic), with some of its territories hacked off to create (or re-create) other nation-states. In the decade following the Great War, Weimar Germany went through two economic collapses, both stemming from Western influences; one immediately following the empire's destruction (about repayment of war compensation), and another following the Great Depression, around ten years later.
After the Cold War, the Soviet Union began to collapse in on itself, in a similar manner to what happened to Imperial Germany, its constituent former "SSRs" broke away into independent nation-states, leaving Russia proper as a republic. At the mercy of the triumphant Western powers, Russia went through economic "shock therapy", resulting in massive inflation and a destruction of living standards. For the rest of the nineties (like Weimar Germany in the 1920s), Russia was ruled by a weak government, resulting in rampant corruption and the selling-off of assets to various new "oligarchs". The Russian default of 1998 created another economic meltdown, socially comparable to what Germany experienced after 1929. As the social and economic conditions in Germany were ripe for someone like Hitler to seize power, the same could be said for Russia in 1999. All it needed was the right man.
Vladimir Vladimirovich Putin and Adolf Hitler as young men were both products of their respective governments.
Hitler was a man happy to fight for his native Austria in the Great War, and thus was emotionally bound to his government and what it stood for; he was devastated by its dismemberment, searching for a new purpose, an explanation, and someone to blame. To the first point, his answer was to restore the "Reich" that had just been wiped out by the Western allies; to the last point, his answer was the Jews.
Putin was a Soviet careerist, making good on his dreams as a youngster to work for the KGB; when the Berlin Wall came down, he was working in East Germany. Similarly, when the Soviet Union collapsed, Putin was searching for a new role, eventually getting Yeltsin's attention and nomination as Prime Minister in 1999, as Russia was still fighting its way through the effects of the default of the previous year.
According to this angle on Putin, advocates of this theory argue that Putin now represents the biggest threat to Europe and Western stability since Hitler, because he wishes to restore Russia to greatness, in effect turning the clock back twenty five years, and the de facto restoration of the Soviet Union.
But there are other very important factors to consider, that make this above theory too simplistic, and largely erroneous.
The Stalin template
I've written before about how Stalin came to power, and the lengths he was prepared to take to keep hold of it. Stalin lives long in Soviet mythology, more because of what advances he achieved in the economy and living standards while he was in power.
Putin no doubt knows all about how Stalin came to power, and ruled the Soviet Union for thirty years until his death. Hitler's motivation to power was to gain revenge on his perceived enemies and to dominate Europe. Stalin's motivation was much more simplistic: the amoral pursuit of power. Stalin couldn't really be said to have an "agenda" beyond his own advancement and preservation; and at this, he was ruthlessly successful and cunning to achieve it. Similarly, while Hitler used the Nazis to dominate Europe military as a geo-political goal, Stalin's domination of Eastern Europe was almost accidental. Stalin was simply in the right place at the right time to advance his interests in Europe in the best way he saw fit. In this way, Stalin could be called a ruthless opportunist, not a megalomaniac like Hitler.
Looking at things in this perspective, Putin's psychology and motivation is more comparable with Stalin than Hitler. While both Hitler and Putin's young careers and outlook came from their governments, both Stalin and Putin's childhoods were similar in more ways.
Hitler was a introverted and socially-awkward youth and young man. Stalin was a brat as a child, getting into fights, hanging out with kids some years older than him, and not taking school seriously; Putin, born and raised in Soviet Leningrad (St Petersburg), was the same. With Stalin, it was discovering Communism as a teenager that straightened him out to an extent and gave him a purpose; with Putin, it was the KGB.
Putin's psychology is therefore bound with the paranoia of the mind of a former spy-master, as well as the cunning of a ruthless opportunist.
It is clear that Stalin is much closer to the template that Putin follows; Stalin, after all, ruled the largest country in the world for half of his lifetime like a "mafia Don", made it second only to the USA, a nuclear power and entered the space race; the fact that he also killed tens of millions of his own people (many more than Hitler) in order to do it, was only a detail to Stalin.
Putin's rise to power, and the manner of holding on to it, follows the same pattern as Stalin. Like Stalin, Putin is in reality an unconvincing speaker; he has used the "cult of personality" like Stalin in order to create a "Putin myth". This serves both to boost his image, but also to boost the image of Russia in Russians themselves; in the same way that "Stalin was the Soviet Union", "Putin is Russia". If Putin is seen as strong, then so, by extension is Russia.
Putin has used ruthless (if modern) methods to achieve and hold power internally; while Stalin killed millions to achieve it, Putin uses modern, legal (but no less politically ruthless) methods. After gaining the financial support of the oligarchs to become Prime Minister and President, he quickly destroyed the power of those same oligarchs who dared to think of themselves as his superior; similarly, the media was brought into line using ruthless methods; newspapers and TV stations being discredited, closed down; people who persisted in displeasing the Kremlin (after stubbornly not getting the message) had a habit of dying in mysterious circumstances or being fatally mugged. And so on.
A clash of civilisations
Like Stalin, Putin's approach to foreign affairs is guided by self-interest and opportunism. Putin's reaction towards the Ukraine Crisis is exactly that: a reaction. There is little indication that there has ever been a long-term plan to restore the "glory of Russia" like some modern-day Hitler, wanting to dominate Europe. Putin simply sees world and Russian affairs through the idea of "spheres of influence"; Stalin thought in a similar way. Stalin occupied Eastern Europe because the opportunity presented itself; Putin has done the same thing with Crimea.
Putin is reacting towards the Kiev government in the way he is because he feels politically threatened by its existence, and the precedent it sets. Stalin got the Soviet Union involved in the Spanish Civil War for similar reasons: he feared the spread of Fascism throughout Europe, and the threat it potentially posed to his position; Putin's support for Yanukovich and the rights of Russian-speakers in Ukraine is framed through his own self-interest. His motivations are far from benign, of course; like Stalin, he has already declared that he is perfectly willing to do whatever is necessary in Ukraine. If, after non-military options have been exhausted, that means invading, so be it. Putin has no moral qualms about his actions; the main thing that guides his actions are their beneficial convenience. War is inconvenient, until it becomes the only method to achieve an aim.
Western fears of him pushing his tanks as far west as Moldova, and fears of aggression in the Baltic States, may be over-stretched in the latter, but not in the former. For Putin, it is simply a matter of what is the most convenient geo-political arrangement for his interests in Europe.
No doubt, Putin would smile at the thought of being compared to Stalin; this is precisely what he would like people to think. For older Russians, Stalin represents stability and strength; his amoral ruthlessness is a side-issue. This issue about how Russians view their government puts it at the direct opposite to a Westerner. A Westerner fears a strong government, because of the West's culture of liberal individualism; a Russian fears a weak government, because of a Russian's desire to feel protected. This fundamental difference in perspective is what marks the emergence of a "clash of civilisations" between an Eastern and Western mentality and world-view.
This also explains why Putin continues to champion "conservative" values against Western immorality, and why his opportune nationalism is him pushing at an open door.
In the same way, Erdogan in Turkey is championing traditional Islamic values. Both Putin and Erdogan are natural authoritarians who have played a very cunning same over the last ten years to preserve and extend their power.
They follow a number of other authoritarian European figures in the last hundred years, and are simply the modern version of an old style of politics.