Answer:
that is what they call him because hes a spartain
HALO
His real name is John as cortana said in halo 4, but they call him master chief
Step-by-step explanation:
hes one of the strongest beings and knows how to take down the covenant with his AI cortana. Ive been playing halo 5 since last christmas and still havent finished it because i played 3 and 4 before 5 :\