Actually...
There's no canonical proof that John is mortal. Lol. But true.
Also
Spoiler spoiler spoiler
John is believed to have a god's "geas" written into him. Which is pretty cool if you know what a geas is.
English
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He's human is he not?
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On top of what gcw said The librarian altered Chiefs DNA and genetics in Halo 4 to raise him to the peak of evolution to counter the didact This means that there could be a strong argument that John may very well no longer be considered human
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At the start. Before he was abducted. Now, he's mostly human. But he's also got a shitload of other stuff in him. Tiger, maybe? I don't know. So he's inhuman. His bones are covered in titanium-his bones. Not the armor. Speaking of which- the armor enhances his abilities. Speed, strength, everything. In fact, the armor has a link to his neural pathways so that even if he's got a broken neck, his armor will do the work for him! Furthermore- assuming that spoiler theory is true... He's got a destiny to fulfill and won't die until he does what he is supposed to do. So until the , he could basically be the Iso-Didact.