What is Communism

Throughout all of history we have seen many different aspects of Communism through the form of countries, many people and historians can agree that they where not accurate aspects and views of Communism. each and every communist leader had his own view and expression of communism, whether it was a mix of two other isms or their own, for example Leninism, Stalinism, Maoism and so on. What do you think is the proper definition of Communism and have we seen something like this before? Which communist leader was the closest to bringing his country to a true communist state?