Imagine a vending machine. Now imagine it has legs. It walks around, sloshing it's contents around inside itself as it waddles across the landscape, gathering more contents. You can go up to the buttons, press them - maybe put money in or maybe you put money in but you've jimmied the coin collector so it simply pops out again into your hand. It's rather like those beetles that have learnt to simulate the antennae movements that will prompt an ant to give up it's crop of food to a fellow ant, since that helps the collony - but since it's a beetle, one who takes while only aping the gestures of giving, the circle is broken.
Is that what the Dunyain are?
Oh no, that's how the Dunyain see you!
You better understand what they are by understanding how they see you! Because from outward appearance they are just another ant...sorry 'person'. All benign, all loving, all waving their antenae in just the right way for you to open your wallet to them. To hand over your children to them.
Also they are part of the speculative fiction (speculative fantasy fiction, no less) 'Prince of nothing' series, by Scott Bakker.
Here's the fan forum and the link, for a few more twisted perceptions on the idea: