During a recent interview with OXN, the actor who plays Agent Locke in Halo: Nightfall, Mile Colter, assured that his character is the star of Halo 5:
Yeah, I’m a playable character in Halo 5.
Once Halo: The Master Chief Collection is released, and then Halo 5 comes out shortly thereafter, you’re basically going to be playing a game with me as the primary character.
I’ll have some cool weaponry, and some cool abilities, because by that time I’ll be a Spartan IV.
Furthermore, Colter hinted that at least part of Halo 5 campaign involves searching for Master Chief, although we don’t know if Agent Locke will be a friend or a foe:
Is he dead or alive? Because that’s usually what a manhunt comes down to, dead or alive, but you won’t know what the purpose of finding Master Chief is [right away].
What’s not known, is whether I’m a friend or foe. The relationship between Master Chief and Jameson Locke is going to be interesting. Because what’s the outcome?
Or what will happen if we do find him, what condition he will be in, and where he’s at mentally. But I’m sure that’ll be a plot twist in Halo 5.
Halo: Nightfall, coming to Xbox One and PC, will be aired via the Halo Channel on November 11.