Looming Villains

[The Dark One]

Sauron is (IMHO) one of the most powerful characters in literature and he barely makes an appearance. Some vague reports from Gollum, a few lines reported by Pippin after the palantir incident, but most impressively, the manifestation of his thought as a storm brooding over the Emyn Muil.

Ingenious characterisation.

Sauron left such an impression on me that I named my first self-purchased cat after him. (Also known as Blackie.) My second cat was Shelob and my current cat is Grishnakh.

 

[wordwalker]

For some readers, Sauron really works-- for others, he's the symbol of cheating the narrative.

A full "looming" villain actually is refusing to develop the character with the usual tools, so no wonder it's at best hard to pull off and at worst liable to alienate some readers. So I'd say it works best when you not only write it well (of course), you also save it for a concept that genuinely calls for that (and that the reader can suspect might go that way just from the back cover), and you make him share the stage with more approachable villains so there's something for everyone.