Nightfall serves as the origin story for Agent Locke. The story is set on one of the broken pieces of Halo from the first game and it tells the story of how he grew up into a Spartan. 343 describes his story as a "superhero origin story." The story of Nightfall is far more tied into Guardians than Forward Unto Dawn was with Halo 4.
Locke is played by Mike Colter in the live-action series. He has already begun to do some motion capture and voice capture work for his character in Guardians. His exact role in the game was not yet revealed by 343 though they promise to answer whether or not he is a friend or a foe of Master Chief exactly one year from now at San Diego Comic-Con 2015.
(via IGN)
