User blog comment:The Milkman/Mass Effect in Retrospect/@comment-24174486-20130416213139/@comment-1786741-20130417172249

I'm with Milkman on this one, the Catalyst WAS the main antagonist. He created the Reapers, started the cycle, and had some sort of control over them. Shepard is trying to oppose all of that throughout the series, so it stands to reason that calling him the antagonist is apt. It doesn't matter that he pulled a "John Henry Eden", he was still the main shadowy antagonist no one knew about until near the very end.