One thing that has always upset me, is how localised it all is in both cases.
(Upset is actually to strong a word, but "concerned me" might be too weak)
What I'm getting at is that in both cases we are lead to believe that these are "World Powers". That all of creation is involved.
But actually Sauron is fighting for Gondor and Eriador, and even Morgoth really seemed only to be concerned with Beleriand. But we are shown that there are other places, Harad and beyond and east of Mordor, and the rest of the now globular Middle Earth that don't come into Sauron's or Morgoth's designs.
Similarly Foul is interested in the Land, but at least the country of the giants and whatever the place where Nom came from was called seem largely untouched by his desires, and we get the impression that there are far more places, continents, etc which are not even mentioned. (The land of the Elohim (?) or whatever they're called, cannot be considered to have a real physical position, but clearly Foul is interested in them.)
I suppose that once Sauron has Gondor, and Eriador, the rest of the world will fall over like dominoes, and the same for Foul and the Land.
I know I'm being picky.
What story has ever been truly global or universal. Whether SF or Fantasy or not, we are always concerned with distances which are fairly easily crossed using the methods or technologies (walking or FTL/Warp) available. (Similarly James Bond can defeat an enemy in one location, once he's found it.) Otherwise the stories would just contain enormous dull gaps for travelling.
Similarly creation happens in hours (for the song of the Ainur) or perhaps days elsewhere, rather than 14 billion years, which would take a very big book.
So another point about Foul/Sauron.
Both involve very long walks/rides/sailings which are actually quite short in real terms, but both are quite closely observed. (with the travels of the Fellowhip of the Ring the most precisely chronicled.)
Oh and someone mentioned than Sauron was a Maia, but, of course, so were Gandalf, Saruman etc.
Were there other creatures on a similar plane to Foul?
Other than, I suppose Covenant. But please don't tell me. I stalled on the Last Chronicles, somewhere in Against All Things Ending . But I may try to finish them one day. (Any advice as to whether it's worth it?)
Wow, I didn't realize more discussions had continued here. I never got any emails about it.
About Sauron being a Maiar - I'm not a Tolkien connoisseur by any stretch, but yes, Gandalf, Saruman, Radagast and even the balrogs were all Maiar. The Maiar could manifest in various forms, had a wide variety of personality types, levels of compassion/empathy and even raw power. It's my understanding that Sauron was quite possibly the most powerful of all the Maiar. I believe Gandalf was known to be apprehensive about his duty to fight against Sauron. He was well aware of how powerful Sauron was.
Concerning Lord Foul and his fixation on The Land:
WARNING - POSSIBLE MINOR SPOILERS AHEAD IF YOU HAVEN'T READ THE LAST CHRONICLES OF THOMAS COVENANT ********************************
In The Last Chronicles, Thomas Covenant would occasionally reminisce about his tenure as the Time Warden after Linden Avery reincarnated him. He remembered traveling through time and personally witnessing events that occurred in the world's past. (Notice I didn't say The Land's past) That world and its civilizations have existed for far, far longer than ours here on this Earth.
I also get the impression that world is much physically larger than our Earth. Stephen Donaldson never really explains how large that world actually is. Or even if it's flat or round. But unlike our world, it is a very magical place so our understanding of the laws of physics don't necessarily apply there.
Lord Foul was trapped in the world almost since the beginning of its creation. Covenant witnessed times throughout its long history where Lord Foul had previously unleashed his machinations in other places far removed from The Land. His outbursts were quite terrible, but to my recollection he never actually came close to destroying The Arch of Time and freeing himself. Then he eventually came across The Land. An isolated place about 1/3 the size of the United States where pure raw Earthpower was bleeding into the surrounding land from the guts of Melenkurion Skyweir. Once he discovered The Land, he decided to park his rear end there and never left after that. The attraction to the raw Earthpower seemed to be too much for him to ignore. This also gave him the opportunity to meet and dominate the Ravers and force them to serve him. Which they didn't seem to particularly mind too much.
The raw Earthpower, the banes buried beneath Kiril Threndor, the Viles, the ur-Viles, the Ravers, the Cavewights - to Foul there was no better spot in the entire world once he became aware of The Land.
I don't remember the exact reasons why Foul never visited the land of the Elohim and wreaked havoc there. I'm guessing they were able to evade him or deflect his notice somehow. I do remember Linden Avery asking why the Elohim never fought Foul themselves and they explained since he was not "of" the world their power had no effect on him.
Were there other creatures on a similar plane to Foul? Well, Foul wasn't exactly a "creature". He is basically the manifestation of the metaphysical forces of hate and destruction. His inverse is the Creator, a being of love, order and creation. They are effectively gods in their particular universe. Were there any more of these beings? Yes, another is introduced in The Last Chronicles and if you have read all the way to Against All Things Ending then you have already heard this being mentioned several times by now. I won't spoil it any further.
Is it worth finishing The Last Chronicles? In my opinion - it's not nearly as good as the first two trilogies but it's worth a read at least once to discover the ultimate fate of The Land and its world.