Board Thread:Metal Gear Solid V/@comment-112.208.72.105-20150901065217/@comment-171.159.64.10-20150917214629

the only one reason that i think why it was the medic, is because of us (every fan), since we took the place of big boss by creating the persona of the "medic", that's why the face customization at the beginning. And since we have been his most reliable and best operative (meaning that we have played through all the saga of MGS and we are the best fitted for the role) is why he choose us, the players, to be his phantom. This is just my thoughts, not anything that is confirmed or story related. :)