User blog comment:The Milkman/Reaper Logic/@comment-3226495-20120430182906/@comment-4558124-20120430213525

Well, we knew about the Catalyst from much earlier in the game, although we didn't know what it was; in addition, the role of a "behind-the-scenes" force was explicitly implied during the Cerberus HQ mission. When you think about it, though, the Catalyst doesn't really represent a new antagonist or conflict: The conflict is the same (Reapers vs. galactic civilization), and the Catalyst really just serves as a sort of "spokesperson" for the Reapers, providing explanations and filling in gaps in our knowledge. It's not as if the Reapers are replaced by the Catalyst as the "bad guys" of the story