[Nick_K]

If you're in a single player game, then there's no harm in making a champion of a unit that doesn't have enough hp. As Endoperez says, he'll probably die sooner or later no matter how you equip him, but it can still be fun to see how well he can do in battle.
If it is SP then MR and resistances are not such an issue. If you're against someone who uses elemental magic you'll want to bear that in mind and equip him appropriately.

So, recommendations... this depends a bit on what magic you have. Also, I assume he has a heroic ability, having won the deathmatch twice. What is it?
What's the base unit? Is this a normal human commander, or something else, possibly with special abilities?

Anyway, equipment... I'm not going to mention artifacts here. You can, of course, get a very powerful commander if you're willing to spend hundreds of gems. The low hp will still lead to him dying though.
Hands are both taken

For the head, I like the Spirit Helmet for the extra killing power. Otherwise, the horror helmet is ok.

Body: I think that the encumbrance on the artifact heavy arnours is too high for a commander on foot. If you're ulm with huge forge bonuses then you might consider the robe of invulnerability. Otherwise the chain mail of displacement is great, and the marble breastplate would be my second choice.
The artifact armour that turns you into a troll would be a fix for the low hp, but you might not be able to get it easily.

Feet: You already have quickness from the champions' trident. You might consider boots of the messenger for the reinvigoration - you can really need it in a long battle.
Otherwise, boots of stone (don't take the marble breastplate with these) would give him a good boost to prot, or the winged boots give the useful fly ability.

Misc:
Lucky amulets are great. I don't think you really need the dancing trident though. The Champion's trident is already long enough for the repel. If you have const 8 then Krupp's bracers are a decent low cost item that gives reinvigoration and extra protection.

Well, hth. Equipping regular commanders with magic items and using them in battle is a very sub-optimal strategy, but if it's fun, then that's fine - I do it myself all the time.