VIDEOS:
The Netherbrain
The Netherbrain reveals to the party that not only did it allowed itself to be enslaved by the Dead Three's Chosen to become stronger with the Crown of Karsus, but it also engineered most of the events of the game, including sharing the knowledge of the Astral Prism to the Chosen and the Emperor's freedom, to achieve its own eventual liberation.
Example of:
The Chessmaster
Example of:
Captured on Purpose