John-117 "Master Chief" was a human, but after going through the spartan program he is no longer marked as a human but as a "spartan supersoldier"
Master Chief was a light skinned with red/brown hair with freckles when he entered spartan training, but As he is now always in armor pretty much, his hair became white and thin, as well as his skin becoming ghostly pale. during Halo 1 and 2 Bungie wanted their hero to be faceless and without personality so he is "easier to get into", However, as the series grew. books were written (official), and other adaptations (movies, anime, comics, etc) gave Chief and the rest of the universe their own personality.
I suggest reading "The Fall of Reach" book. It explains the backstory very well and gives some insight to the spartan program.
here is some more source and reading from the off the wiki about John-117. click me