1) My quote is from wikipedia.
2) Stalin was a socialist who wanted socialism in one country. Which is to say, National Socialism. He had an alliance with Adolf Hitler (another National Socialist).
3) Trotsky thought Stalin didn't go far enough in his communist beliefs. The folks who think Hitler was "right-wing" are folks who were further Left than Stalin. That's Trotsky.
4) The Fourth International carries the banner of Communism today and they are far more active and influential than people think. They promote Trotsky's belief's.
People shouldn't pay attention to Marx. Marxism is truly dead. But Trotsky, Gramsci, and the Frankfurt School are (sadly) alive and kicking.