Black Mantis
Member
Pretty much... everything. He's entirely defined by his species. You don't learn why he's important, who he was, what he did. He's "a Forerunner" and that has to be enough.
He wants to prevent humanity from attaining the mantle... but to what end? As far as we know, he's alone in the universe. Once he kills off every human, he'll be left sitting in his floating ball, surrounded by robot dogs and "inferior" species. Why would he want that? It's like screaming "IF I CAN'T HAVE IT, NO ONE WILL" in the form of a galactic genocide. (ancientmanyellsatgalaxy.jpg)
As I said before, given that the Halo games view things from the playable character's pov, you're not going to get all that unless The Didact were to stand around and explain it all to MC as he held him captive. That's the role of the terminals, and I personally felt that worked in regards to the Didact. Their failing in Halo 4, was to have those segments tucked off in the Waypoint app.