So, re-reading the Foreword to THE LORD OF THE RINGS last night I was struck by a familiar passage I realized I haven't fully thought through before. After pointing out that his book is not a roman-a-clef allegory of wartime politics of the World War II era, Tolkien gives an alternative summary of how things wd have gone in his book had that been the case:
The real war does not resemble the legendary war
in its process or its conclusion. If it had inspired or
directed the development of the legend, then certainly
the Ring would have been seized and used against
Sauron; he would not have been annihilated but
enslaved,* and Barad-dur would not have been
destroyed but occupied. Saruman, failing to get
possession of the Ring, would in the confusion
and treacheries of the time have found in Mordor
the missing links in his own researches into
Ring-lore, and before long would have made
a Great Ring of his own with which to challenge
the self-styled Ruler of Middle-earth. In that conflict
both sides would have held hobbits in hatred
and contempt: they would not long have survived
even as slaves.
Although Tolkien does not name this 'self-styled Ruler of Middle-earth', he offers some clues as to who he, or she, might be.
First, we know that it's not Sauron, who has been defeated and imprisoned.
Second, we know it's not Saruman, since he's acting in opposition to the Ruler as his or her rival.
To this I wd add that the Ruler wd have to have (1) an opportunity to seize the Ring and (2) the stature to be able to wield it**
I therefore come up with a list of seven candidates:***
*This of course wd have been repeating Ar-Pharazon's mistake
**or it wd just wind up (briefly) in the possession of another Gollum.
***I exclude Bombadil from this list, for reasons I assume will be obvious