Terabithians
The Terabithians were briefly mentioned in the novel but play a big part in the 2007 movie adaptation. They are the creatures that live inside Terabithia, they are nice and peaceful beings. The 'Bird Woman' and 'Soldier Fairies' are two examples. It isn't clear who invented each Terabithian, but in the 2007 movie, it is Leslie that created the soldiers from dragon flies. One could assume that Jess created the rest of the entire civilization by the fact that when they are shown, Leslie is already dead.
Read more about this topic: Creatures Of Terabithia