'They [Orcs] are not based on direct experience of mine; but owe, I suppose, a good deal to the goblin tradition (goblin is used as a translation in The Hobbit, where orc only occurs once, I think), especially as it appears in George MacDonald, except for the soft feet which I never believed in.' JRRT letters

'Now in these subterranean caverns lived a strange race of beings, called by some gnomes, by some kobolds, by some goblins. There was a legend current in the country that at one time they lived above ground, and were very like other people. But for some reason or other, concerning which there were different legendary theories, the King had laid what they thought too severe taxes upon them, or had required observances of them they did not like, or had begun to treat them with more severity, in some way or other, and impose stricter laws; and the consequence was that they had all disappeared from the face of the country.

According to the legend however, instead of going to some other country, they had all taken refuge in the subterranean caverns, whence they never came out but at night, and then seldom showed themselves in any numbers, and never to many people at once. It was only in the least frequented and most difficult parts of the mountains that they were said to gather even at night in the open air. Those who had caught sight of any of them said that they had greatly altered in the course of generations; and no wonder, seeing they lived away from the sun, in cold and wet and dark places. They were now, not ordinarily ugly, but either absolutely hideous, or ludicrously grotesque both in face and form.

There was no invention, they said, of the most lawless imagination expressed by pen or pencil, that could surpass the extravagance of their appearance. But I suspect those who said so had mistaken some of their animal companions for the goblins themselves -- of which more by and by. The goblins themselves were not so far removed from the human as such a description would imply. And as they grew misshapen in body they had grown in knowledge and cleverness, and now were able to do things no mortal could see the possibility of. But as they grew in cunning, they grew in mischief, and their great delight was in every way they could think of to annoy the people who lived in the open-air storey above them. They had enough of affection left for each other to preserve them from being absolutely cruel for cruelty's sake to those that came in their way; but still they so heartily cherished the ancestral grudge against those who occupied their former possessions, and especially against the descendants of the king who had caused their expulsion, that they sought every opportunity of tormenting them in ways that were as odd as their inventors; and although dwarfed and mishapen, they had strength equal to their cunning. In the process of time they had got a king and a government of their own, whose chief business, beyond their own simple affairs, was to devise trouble for their neighbours. It will now be pretty evident why the little princess had never seen the sky at night. They were much too afraid of the goblins to let her out of the house then, even in company with ever so many attendants; and they had good reason, as we shall see by and by.'

Why The Princess Has A Story The Princess and the Goblin, George MacDonald

'Well, to be honest, it is a goblin's weakness. Why they come so soft, I declare I haven't an idea'.

'Specially when your head's so hard, you know father'

'Yes my boy. The goblin's glory is his head. To think how the fellows up above there have to put on helmets and things when they go fighting! Ha! Ha!' The Goblins

[there seems to be an issue concerning fingers too] 'Indeed, he had not been able even to satisfy himself as to whether thay had no fingers, although that also was commonly said to be the fact.' The Goblins

'For, while each knight was busy defending himself as well as he could, by stabs in the thick bodies of the goblins, for he had soon found their heads all but invulnerable, the queen...' The Goblins In The King's House