Master Chief is an integral component in the Halo franchise. He’s been the main protagonist in nearly every game, but not in Halo: Reach because it takes place before the first game, Halo: Combat Evolved. However, you can find Master Chief in the game.
To find this easter egg, you need to jump on over to the final mission, Pillar of Autumn.
You can find it at the end of the game when you’re defending the Pillar of Autumn while it prepares to leave Reach. You want to proceed through the mission normally, no need to do anything special or fancy along the way.
When you reach the final cutscene, which is the Pillar of Autumn taking off, move your right thumbstick to the right, and hold it there. You want to push on it and hold it throughout the entire cutscene. Eventually, when Captain Keye’s Pelican touches down inside of the Pillar of Autumn’s hanger, the camera shifts to the right, and there’s a Spartan in a cryotube.
There was a bit of debate when this game first released if this Spartan to be Master Chief, due to the next part of the Pillar of Autumn’s journey takes to them to the start of the first game, Halo: Combat Evolved. However, when Halo: Reach first released in 2010, the Halo‘s creative director, Marcus Lehto, confirmed that it was Master Chief, John, at this moment in 2010’s issue of Game Informer.