Undead are, simply put, among the most horrific things one can think of. Can you imagine anything more frightening than a being which is dead and yet still walks? Can you imagine the horror of being faced by the hollow shell of being, a hollow shell which must feed?
Unseen and striking from suprise, this creature is on its way to becoming a legend.
Awakened by a Curse, fed by the cries and anger of children, this creature now roams the world.
Think of any bizzare life-form, WHATEVER life-form that lives a not-so-standard way. Not the way common sense would expect it. Make it in some way logical or not, just forget the boring everyday logic.
The Eternals are one of the few races who survived the awakening of the Gods and the fall of Prime Creation. They were solitary, but powerful, weavers of essence and were locked in a bloody war with the Other Ones, another race which survived the Gods.