Sergeant Johnson survives at the end of Halo 1 after the ring blows up. This is proven by him hugging the elite at the end, and then being in Halo 2.
He "dies" in Halo 3, but the person who is killed by Guilty Spark isn't actually Johnson, as Johnson is black, not white.
He then appears on the level Shutdown in Halo 4, further proving he didn't die in Halo 3.
He then changed his name to Locke and had facial reconstruction as a disguise, and will be hunting down Chief in Halo 5.
Prove me wrong.
Pro-tip:[spoiler]You can't. [/spoiler]
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I thought maybe Locke is Noble 6. As far as we know he's the only other spartan on Chiefs level. He has connections thru ONI and it isn't 100% confirmed he died on Reach. His name was never given out back in Reach so it could be an option.