in most of the other threads, we've come pretty much decided to go with king heroes. Now we need to think of thier abilities, and which go with which civ. most importantly, when do they appear (when are they built) and what happens when they die.

What i propose is a national wonder which would create the king unit once it is built. this would come halfway through the game. if you king unit should die, then there should be major penalties (angry faces, loss of production, loss of a couple outer cities, etc...)

List:
Angmar: Witch-king
Dunland: Saruman
Rohan: Helm Hammerhand
Arnor: Elendil
Shadow: Sauron (reason i'm saying this is that we have art for him)

I'll edit this list with your ideas.

Elros could be the king of the numenorean people...

For the Arnor: Elendir
Galadriel should also be a spellcaster...

what about melkor?

Melkor is too powerful. The King unit for the Shadow would probably be the Witch-king, just because he isn't a Vala or Maia.

See the topic for The Shadow (Some Shadow Mecanics), it explains how I'd like Sauron to be. And here are my ideas (I don't know how they could be done, and not even if they could be done):
Each civ would start with it's king unit, and if possible we should have a king unit for each leader (so, if you are Aragorn, you have Aragorn, if you are Elendil you have Elendil).
I'd have 2 kinds of king units (apart of special ones, like Sauron, Saruman, and the Witch King): warrior (better early game; more like a normal hero) and commander (good through all the game; more like the Great Genneral, maybe replacing it). The leaders of each category for each civ would be equal (maybe we should have just 2 units for each race, but with various names like Great People - maybe we could actually make them some kind of GP).
When it losed a battle, it would only be badly wounded and return to the capital - it respawns there, but your units suffer damage from low morale. (Sauron has a slightly different system... see his topic).

I think either both king units should be good through the entire game, or (for at least the warrior) there should be something like the Civ3 Sengoku scenario did - certain techs allow you to upgrade your king (Daimyo in Sengoku) and give him a strength increase, thus increasing useful life.

(I actually lost my first Sengoku game by using my Daimyo as an offensive unit. :P)

I would like the dog or the dragon..,

I would like the dog or the dragon..,

???

About the units being good the whole game, well, they could be, but what is more useful: an extra unit in the start of the game, when you have few, or late game when you have a lot of them (suposing they have the average strength of that age; probably they will be a little weaker, but with bonuses against certain kinds of units).

With the upgrading idea, you get both.

No, because an extra warrior from the start of the game is +100% units, while late game may be just about 1% of the row number...

True, but he will still be useful as a defensive unit in the late-game, whereas if you had a warrior hero with no upgrades, then he would be entirely useless.