SimonAtford wrote:. . . as I understand it Tolkien meant orc and goblin to be interpreted as two names for the same creature. Not really a criticism of the film as I think it works. The slightly comic goblins of The Hobbit do seem quite different to the more menacing orcs of LotR. It does however beg the question of what happend to the goblins before the events of the movie version of LoTR.
In the cosmology of Arda/ME goblins are orcs and orcs are goblins, but over the course of the timeline (tens of thousands of years) there are cultural and physical increments in their development.
Essentially the orcs/goblins of the LotR are from a different strain to those in TH. The ones you see in the Trilogy are largely those who have remained directly under the sway of Sauron (and Saruman as influenced/corrupted by him). Away from Moria/Khazad Dum the goblins/orcs of the Misty and Grey Mountains as seen in TH are feral and remnant populations that have been separated from Mordor at earlier points in time in the First Age (we're in the Third Age in the trilogy and TH) and around 500 years earlier when the Witchking's realm of Angmar fell.
Orcs are not necessarily completely defined in either of the books - the Uruks (the Isengard orcs, but also of Mordor) are of a different 'strain' that arose when the Witchking fled to Minas Morgul and needed bigger, stronger goblins to fight the men of Gondor so they are essentially goblins 'bred' for size, musculature and intelligence. In the more ancient times there were also very large aggressive goblins but these were slightly different in nature, being 'Boldogs' - evil spirits who took on a grossly exaggerated goblin form and led the normal ones into battle. These were a little like the Eagles (the supersized ones) in that they were apparently immortal but 'fixed' in their shape. It is possible that The Great Goblin and Azog (and Bolg) were Boldogs rather than regular goblins, but in TH they were leaders who were, at that point, independent of Mordor and Sauron and kings in their own right.