Nocker was originally a one of the original fae who was transformed when he deliberately sought to change the Dreaming, creating the Gate of Ivory. The other fae became Trolls at the same instant.
Nocker shares with House Dougal the ability to craft new objects, such that the crafted object has a new nature. What Nocker alone can do (though it doesn't happen on demand) is imbue an object he crafts with its own Dán.
Nocker's approach to the Dreaming goes against that of the Trolls, for the latter are the embodiment of the rules of the Dreaming. Nocker constantly tries to do something, Troll says he can't (meaning that it's not possible given the rules), Nocker tries anyway and fails. He resolves to make something which will keep Troll out of his hair, to boss Troll and all the other Fae around.
He comes across a great graveyard, in which lay the skeleton of a mighty Dragon (in fact, this was the bones of Sidabras, the Last Silver Dragon). Taking two horns, Nocker builds the Gate of Horn. He seeks to 'summon' a power which will give him mastery over the Trolls but gets the Sidhe House Founders instead.