The society in 1984, although fictional, mirrors the political weather of the societies that existed all around him. Orwell's Oceania is a terrifying society reminiscent of Hitler's Germany and Stalin's Soviet Union — complete repression of the human spirit, absolute governmental control of daily life, constant hunger, and the systematic "vaporization" of individuals who do not, or will not, comply with the government's values.
Orwell despised the politics of the leaders he saw rise to power in the countries around him, and he despised what the politicians did to the people of those countries. Big Brother is certainly a fusing of both Stalin and Hitler, both real and terrifying leaders, though both on opposite sides of the philosophical spectrum. By combining traits from both the Soviet Union's and Germany's totalitarian states, Orwell makes clear that he is staunchly against any form of governmental totalitarianism, either from the left or the right of the political spectrum.
By making Big Brother so easily recognizable (he is physically similar to both Hitler and Stalin, all three having heavy black mustaches and charismatic speaking styles), Orwell makes sure that the reader of 1984 does not mistake his intention — to show clearly how totalitarianism negatively affects the human spirit and how it is impossible to remain freethinking under such circumstances.
