Halo 4 includes a few Easter eggs, one of which is voice-over work from Conan host Conan O'Brien and sidekick Andy Richter, and a GameFront video demonstrates how to find them in the game.
The two comedians provided the voices for two guards standing in a loading bay. Here are the directions to their spot, courtesy of GameFront:
Conan's voice-over can be found in Mission 6: Shutdown. You'll find two marines standing near a forklift in the large loading bay, past a row of Warthogs. You'll be on the search for a Pelican Dropship, don't board it just yet. When you find the two masked marines, they'll remain silent. Just wait, they’ll eventually start talking!
O'Brien and Richter visited 343 Industries earlier this year for a Conan segment that aired in mid-April and included footage of their voice-over recording sessions.