Stalin did not defeat Hitler. The Soviet people did this in spite of Stalin's incompetence and some stupid strategic moves that he made.
It is really a stupid move to equate a people with the person who happens to be holding the current position of power. Do you equate Ukraine with Yanukovitch? Probably not. Then why would you equate the Soviet Union with Stalin or equate Russia with Putin or the USA with Obama. In all these countries there are many, many actors. Yes Stalin did pull many of the strings in the Soviet Union, to the extent that any person in power can pull strings.
But remember that old Chinese saying that the mountains are high and the emperor is far away? That applies to any large country, and it means that Stalin controlled far less than people attribute to him.
Of course, in modern times it means that Obama, Yanukovich and Putin also control a lot less than most commentators would claim. For instance I recently read a news piece in which it claimed that Putin ordered Russian troops into Georgia. In fact, the president of Russia at the time, Dmitri Medvedev ordered the troops in. And someone claimed that Putin is responsible for killing stray dogs in Sochi. In fact it is the town mayor and city council that is responsible. Many Russians are aghast and have mounted a campaign to move dogs around so that the killers can't find them, and have also set up several dog shelters to feed (and neuter) the dogs. Putin has nothing to do with any of this. It is part of the swirling of events in a complex society.
All world events like WWII are the same and anyone who digs in the details learns that the notable figures (generals, presidents, etc) are really just politicians who claim responsibility for the work of other people. These so-called great leaders alternate between urging their henchmen to carry out some action, and running to the front of the parade over which they have no control. They are less powerful than they seem.