Halo 5's secret Spartan is Agent Locke, and his story will be revealed in Halo Nightfall

Halo 5: Guardians' mystery Spartan is Agent Locke, and the solider's story will be told in producer Ridley Scott's episodic series Halo Nightfall.

When Microsoft released the first image of Halo 5: Guardians (above), the Spartan with a blue visor appeared as if reflected above Master Chief. Halo: The Master Chief Collection, the four-game bundle of numbered Halo games, will include access to Halo Nightfall.

Locke will play "a key role in Halo 5: Guardians," general manager and 343 Industries studio head Bonnie Ross said.

"We're using Halo Nightfall to basically tell his backstory and tell his origin story," Ross said during a Halo-themed meeting at E3 2014. "You don't have to watch this, but knowing this will kind of tee you up for all the new things that are going on in Halo 5: Guardians."

Nightfall is in production now, Ross said. Shooting just finished in Ireland and has moved on to Iceland. At San Diego Comic Con this year, 343 will reveal more about how the show and the game will interact.

Microsoft is also partnering with Blur Studios to create animated stories in The Master Chief Collection's remastered version of Halo 2. Unlockable by finding terminals in Halo 2 like those found in the remastered Halo: Combat Evolved, their stories will follow Halo 2's second playable character, the Arbiter, and will also bridge the gap between 2013's Halo 4 and 2015's Halo 5: Guardians.

Blur will also produce a prologue and an epilogue to the story 343 teased in the E3 trailer below. Delivered as a message from the Arbiter to Agent Locke, it also includes a brief appearance from the Spartan, who must "walk in his footsteps" to find Master Chief.

"The goal there is to drop you right off at the doorstep of Halo 5: Guardians," Ross said.