Stalin, Mao, and I think Castro (I don't know about Qaddafi) were totalitarians, single parties that exercised total control. Authoritarians are people like Putin, an undemocratic dominant power among some competing power centers (though maybe Russian politics has shifted into totalitarian).

Maybe we can say that authoritarians use the system to control things; totalitarians build a system of only themselves (or their party, such as the Soviet and Chinese Communists).