I would consider some sort of messiah or Christ figure. Start off by circulating some prophesies of the chosen one, the one who will free us, the peace-maker, etc. Then you can either introduce a fully grown person or introduce a baby. If fully grown, then I would use the Argrath ambiguity to allow the characters to compete to be the messiah through heroquests and such. If a baby, then I would have the characters protect the baby to adult-hood (which might be vastly accelerated). The Christ paralel might be closest for overcoming the Kingdom of War. Since the KoW worships death gods, maybe the messiah teaches resurrection. If you don't like the Christ parallel, perhaps the messiah puts the death gods in their places, like many culture heroes do at the Dawn. Implicitly, that means putting the KoW back in the Underworld, "where it belongs."
Chris