Human, with HEAVY military cybernetic enchancements from previous era (implemented by some ripperdoc; crud, ugly, barbaric looking even prosthetics and other implants) - deemed fascinating by LEGION, feared by the rest (yes, even Jack, Grunt or Zaeed) and coz of his cold mind and heart, more a machine that human. Calculating, ruthless and callous...and unforgiving. Extremely strong and durable, unnatural stamina.
Only some devious thought makes him Shepards subordinate.
Husks cant see him and avoid him as obstacle.
Cannot be hacked or infected with alien tech.

but somewhere in this void a spark of humanity flickers still...