What did Sauron look like?

Sauron was a Maia, and in his early career this meant that he had the ability to change shape at will: in the First Age, he seems to have had a generally human form (he's variously described as smiling, laughing, standing and so on), though in his battle with Huan he was able to shift freely between the forms of a wolf, a serpent and a flying vampire. In the Second Age, during the time when the Rings of Power were made, he took on the semblance of a noble teacher. However, his shape-changing abilities were not limitless, and after the Downfall of Númenor they were severely curtailed:

After his defeat in the War of the Last Alliance, things became even worse for him, and he lost his physical form altogether:

This was in the last year of the Second Age. The story of The Lord of the Rings is set more than three thousand years later, in the closing years of the Third Age, but that book includes only the slightest hints of a description of Sauron. No doubt Tolkien kept Sauron in the shadows for good dramatic reasons, leaving it to the reader's imagination to create something darker and more fearsome than a mere description could convey. This literary device has left behind something of a puzzle: what actually did Sauron look like? For that matter, did he have any kind of physical body at all?

The question is made more complicated by the recurrence of the image of the Red Eye, which often appears to signify Sauron. In some places, this is clearly used as a symbol, but in others it actually seems to be - at least partially - a physical description. This is the Eye that Frodo saw in the Mirror of Galadriel:

This has led more than a few readers to interpret the Eye absolutely literally, to the point where Sauron is imagined simply as a burning eyeball. The most notable of these readers, of course, is Peter Jackson, who used the motif of the glowing eye throughout his trilogy of movies. Indeed, at one point in the movie The Fellowship of the Ring, Saruman explicitly states of Sauron that 'he cannot yet take physical form' (though nothing comparable to this appears in the book).

This isn't an unreasonable position to take. There are numerous references to the Red Eye as a symbol for Sauron, and in places it's difficult to tell where the symbol ends and the physical description begins. For example:

On the other hand, there are several references to 'the red eye' that clearly have nothing to do with Sauron at all. There's an example of this in the following quote, where the 'red eye' is in the Tower of Cirith Ungol:

Here, the idea of the red eye embodies the unsleeping watchfulness of Mordor, and has no direct relation to Sauron. In fact, there are reasons to think that the capitalised 'Red Eye' is simply an extension of this metaphor. For example, speaking of Sauron's fingers, Gollum - who has apparently seen the Dark Lord with his own eyes - says:

It follows that if Sauron has a Black Hand, he cannot merely be a Red Eye. There seems to be at least one metaphor in use here. Actually, there is quite a weight of evidence within The Lord of the Rings that Sauron had some kind of physical form:

The characters who say these lines (including his own Orcs) all seem to believe that Sauron could easily travel from one place to another. In particular, Aragorn seems to believe that Sauron not only has a physical form, but that it would be possible to do harm to that form:

Curiously, this line was used word-for-word in the movie version of The Return of the King, despite the fact that Sauron was depicted there as an apparently immobile glowing eye.

If we move to Tolkien's letters, it becomes hard to avoid the conclusion that Sauron did, indeed, have a physical shape. For instance, there's a reference there to:

The War of the Ring started in the year 3018 of the Third Age - it's hard to imagine that after more than two thousand years, Sauron still hadn't formed a new shape for himself. There's another reference among Tolkien's letters that goes even further, to the extent that it effectively settles the discussion:

This is from a letter specifically discussing the events at the end of The Lord of the Rings, so there's really no question that it describes Sauron as Tolkien saw him then. In fact, it seems that the huge armoured Sauron that appears at the beginning of the movie The Fellowship of the Ring probably fits Tolkien's vision rather better than the image of a glowing eye.