Here is the trailer for the upcoming digital series, Halo: Nightfall. This is not the series being produced by Steven Spielberg. This series is being produced by Ridley Scott.
It will focus on the origin of Agent Locke, the other Spartan on Halo 5 reveal image. Rumors also suggest that Agent Locke will be playable in Halo 5 as well. Could we see a Halo 2-esque back and forth switching between Locke and Master Chief similar to playing as Chief for a few missions, and then playing as the Arbiter in Halo 2? My guess is that this is what we will see in Halo 5, or at least something similar to this.