hows about a fire/dark corruptor. while your heroe is someone that saves liives the corruptor can be the opposite and maybe do something to tie them in.
How about a Tech Necro/Force Field Mastermind? He (or she) could have been involved in the attack that destroyed the Asclepius Program that was the source of Medic-001's suit. They stole an earlier prototype that could not heal, but could reanimate dead tissue as well as generate protective forcefields. Badly injured during the attack they were forced to put on the prototype suit to survive even though it had not been fully tested or calibrated to their biorhythms.
Unbalanced biofeedback from the prototype suit has driven them mad, and they are obsessed with capturing Medic-001 to gain access to the perfected Asclepius technology.
Name ideas could revolve around imagery such as graverobbers/bodysnatchers or reanimation.
I hope this sparks some ideas for your arch-nemesis.
(jaw drops) that is the best suggestion I have ever heard
This is Greyscribe we are talking about here. Did you REALLY expect anything less?
Hell, him coming up with a bad idea is about as likely as me coming up with something actually funny and not just so stupid that people laugh AT me.
...What? Stop looking at me that way! I am NOT paranoid!
<.<
>.>
*TWITCH*
Awww shucks, tweren't nuthin' 
I have plenty of bad ideas Prodiguy, I just bury them so deep no-one ever finds out about them 
Glad you liked it Medic001 - your origin story gave me plenty of hooks to work with. The existence of the final suit being issued to highly trained medical staff suggested a long development cycle before Medtech's destruction so the existence of prototypes wasn't a big stretch. Healing living tissue (very media-friendly) isn't too far away from reanimation (not so easy to spin) so that suggested the whole necro theme for a failed Asclepius prototype. Then any good arch-nemesis has to have strong ties to the hero, often from the very beginning of their careers so putting them at the scene of Medtech's destruction seemed obvious.
Here are a few name ideas for good measure:
Necrocide
Necrosis
Terminal Force
Terminus Null
Bodyfarmer
Aberrant Cadaverer
And I'd recommend the 'omega' symbol for the chest insignia.
I need help coming up w/ an "arch-nemesis" for my toon (you can read bio here
any suggestions would be helpful (he is an emp)