First off… This voice sounds extremely like Saren Arterius from Mass Effect so its assumed that its voiced by Fred Tatasciore.
Second, We probably all realize that it is the main antagonist in Halo 4 (maybe the whole trilogy). The Forerunner symbol that was shown at the end of the Stage Demo looks very similar to the Didact’s symbol but upside down. Symbol Comparisons before symbol flips and Symbol Comparisons after symbol flips
So its hinted that the last known Didact may play a role in Halo 4 somehow as the bad guy but its unlikely since he was never known to be a bad person in the past.
So this is all Speculations, not confirmed as of now. Give your opinions about this matter of discussion.