It took a few weeks for the majority of fans to suss it out, but it seems that Key & Peele's own Keegan-Michael Key is providing the voice talent for Halo 5: Guardian's alternate-reality game.
The hub for the ARG appears to be a page on Tumblr, titled Hunt The Truth. There you'll find the audio logs for Benjamin Giraud, a fictional investigative journalist and war correspondent on the trail of "the origins of modern-day superhero Master Chief." Audio logs initially appeared on Soundcloud, but now they're being fully integrated into iTunes as well.
The very first episode is embedded below.
In the performance of the podcast, Key's portrayal of Giraud is nearly lyrical in its praise for the legendary Master Chief. But each episode amps up the mystery, and the podcast's soundtrack as well as Key's breathy, almost nervous delivery all appear to be leading up to something dreadful.
"A few months ago I was hired to do an in-depth profile on the Chief — exclusive access, the whole thing," Key, as Giraud, said. "Since then I've gotten to talk to a lot of people who claim they know the real Master Chief; the boy, the soldier, the hero. The traitor?"
For a weathered war correspondent, whatever he uncovered about the Chief has him spooked.
Incidentally, these same words — boy, soldier, traitor — have been found inside various layers of the ARG, which is being explored most rapidly on its dedicated Reddit page. The repetition of those words in the podcast seems to be a marker for those playing along, and no doubt clues will be shared through the audio performance in the coming weeks. For those uninterested in the day-to-day grind of the ARG however, the podcast is high-quality enough that it will probably be a good experience for Halo fans on its own.
You can see the latest Halo trailers, which offer a conflicting narrative of the same catastrophic event, here.