Good question! I was gona add him to my "What IS that?" thread when he came out.
The problem with Man-E is that he's had some pretty goofy bios over the years. They always peg him as an actor, but what child is gona think of that when you get him in hand? I guess he's shown to impersonate people in some cannons, so the suit could be a Zartan-like hologram suit that allows him to take anyone's form. But...you'd think that would be displayed better, you know? His obvious feature is faces! When I was little, this guy was a Frankenstein FREAK, you know? I always imagined he was a horrible technological experiment where they tried to fuse two bodies together. Wasn't working, so they used one body and built a mechanical suit around it, then fused the heads. The robot head would be a final "control unit" to control both sides so that neither goes insane from the process. In the end, when he's brought to the good side, he uses his different "personalities" like he does in most cannons: beast for strength and other beastly things, human for normal human stuff, and robot for all those technical things.
...course none of that works in the standard cannon, but I'm gona ignore all that actor stuff.