Eiddileg took Taran, Eilonwy, Fflewddur Fflam, Gurgi, and Melyngar prisoners for a short time before he released them along with food and a guide named Doli. Before the travelers left his throne room, Eilonwy gave him a kiss on the head. When she left, he could be seen smiling happily, therefore providing a hint that like all Fair Folk his gruff or defensive exterior masked a good and kindly heart.
Eiddileg was often referenced as giving orders to his people, or as being informed of news of the struggle against Arawn, but the Companions never saw him again. During the events of The High King, the Dwarf King -- on hearing of the Death-Lord's impending attack on the Sons of Don -- ordered Doli to lead a troop of some hundred dwarf warriors to aid Taran in the Hills of Bran-Galedd.
At the end of the series, as enchantments vanished from Prydain, Eiddileg commanded the Fair Folk way posts closed, the entrances to his kingdom sealed shut from the world of men. And so magic passed from the land.