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Goblin
From Discworld & Pratchett Wiki
There are two mentions of Goblins as a distinct race living on the Discworld, and both occur in Equal Rites.
In a discussion about Dwarfs keeping up the old traditions, it is said that rich Dwarfs in non-Dwarfish professions, such as the clerical trade, willl employ goblins to do nothing else other than hit small ceremonial anvils with small ceremonial hammers all day, purely to create the sort of atmosphere in which a Dwarf finds it easy to think.
Secondly, Gnolls are explicitly described as a sort of stone-goblin. (Use of the word "goblin" supports the position that originally, Terry Pratchett intended them to be the Discworld analogue of Tolkien's Orcs, as they are vicious, sadistic, murderous, and attracted to filth). However, by the time of Jingo, all that appears to survive of this original concept is the attraction to filth and possibly a little residual cruelty.
Ponder Stibbons once played the role of Third Goblin in a school play.
[edit] Annotation
On the change of the nature of Gnolls through the books: there is a famous critical comment on Terry Pratchett's work, comparing him to Tolkein, but with the caveat that "in these Détènte-driven days, Pratchett has no horrors waiting to emerge from the East".
It could just be that an Orc-analogue simply wasn't needed - look at the way Elves have filled the niche for a non-human Other, which is inimical to mankind - and having introduced Gnolls in an earlier book, they simply got recycled to fill a different socio-ecological niche more suited to Discworld.

