Agent Locke is a new character to the lore of Halo that will make his first appearance in the live actions series, Halo Nightfall, however, the actor that plays Locke suggests the character will play a big part in Halo 5: Guardians as well.
In fact, according to actor Mike Colter, the man who plays Agent Locke, the main protagonist in Halo 5 may instead be Agent Locke instead of the Master Chief.
Colter revealed in a recent interview with X-One magazine that "I'm a playable character in Halo 5." Colter went on to explain that, "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."
"What's not known, is whether I'm a friend or foe," Colter suggested. "The relationship between Master Chief and Jameson Locke is going to be interesting. Because what's the outcome?
We can't really confirm or deny any of this information at this point as 343 Industries have yet to respond, but it would certainly turn the scales if Agent Locke ended up becoming the main protagonist to the current Halo trilogy.
It wouldn't be the first time players have been able to play another character in the Halo franchise - in Halo 2, half of the campaign missions were played through the eyes of the Arbiter.