after finishing halo 3 in legendary, i dowloaded the marathon games, and at the mains screen says:

"Relieve the Dream"

Also in the manual says: " You can almost imagine the face of a wicked computer with its eyes wide and its lips folding out in a grotesque smile. A smile which reminds you of something from your past, but you can't remember exactly what it is. "( page 3)

You pull out your pistol, and pound the switch to open the door. Oddly , this is familiar to you, as if it were from an old dream, but you can't exactly remember... (page 4)

and also in the series it is told that you are not a human and there is all this thing about a missing cyborg( i think thry are referring to SPARTANs) and it is possible that you are him.

Also if you play the marathon series( they are free now) you'll notice that your hand looks a lot like MC's , thats mainly because you are usin a Mark IV or V armor , like MC...

for more info: http://marathon.bungie.org/story/you.html