I'm a big fan of the concept of the Ten Who Were Taken from Glen Cook's The Black Company series; an epic 10-volume tale of dark, military fantasy and one of the godfather achievements in the sub-genres of dark fantasy and military fantasy alike. My Heresiarchy of the Twelve is not unconsciously modeled, at least in some respects, off of the Ten.
I've also been a fan of a lot of the Warhammer World fiction. Nagash, in some ways, who I've referenced here before many times, can be seen as analogous in many ways to the Dominator; a leading sorcerer who created other sorcerers, who's black legacy still haunts the world many centuries or even millennia after his initial time of power. I've been reading Mike Lee's Nagash trilogy lately (about time too; I've owned the books for many years.) The first of the books, Nagash the Sorcerer I found somewhat difficult; the plot was convoluted, the characters less than compelling, and the time frame and politics made for somewhat stodgy reading. Because I had been a fan of the "lore" of Nagash for many years (dating back to my picking up a White Dwarf way back in the early to mid 90s that described his "secret history" in textbook style) I was anxious to see this committed to novel form. The first book was disappointing, though—and I let the series sit fallow for quite some time.
Only recently have I finally picked up the second book, Nagash the Unbroken and quite honestly, it is tons better. It alternates between far fewer point of view characters; Neferata being one of the main ones, and her drive to essentially create the vampiric race in Lahmia with the aid of a captured Arkhan the Black is fascinating. Every other chapter then turns to Nagash, who having faced a crippling defeat in Nehekhara, has now wandered over to Cripple Creek and on his way to becoming more than simply a self-made vampire/sorcerer lord, but rather the master sorcerer Nagash the lord of the Undead.
One of the things Warhammer does quite well is to not really explain everything—in spite of the fact that they're turning what was a few pages of textbook style history into a novel trilogy, there are a lot of holes in the setting. Stuff that doesn't quite add up. Stuff that contradicts other stuff. Mythology that refuses to be classified and nailed down. Stuff like that. This deliberate uncertainty principle gives it a very verisimilitudinistic feel; as events are removed from the current continuity in time, more uncertainty about what actually happened and what stuff actually means seems to be de rigour. This is, of course, often the opposite of what many high fantasy fans are used to, where thousands of years of detailed timelines and maintained status quo seem to be common.
I also really like, of course, the notion of digging up the past that should be better off left alone. This is a very Lovecraftian concept, but it is also one of the main drivers behind some of the Black Company novels (Bomanz, the wizard who "accidentally" unleashed the Ten Who Were Taken back on the world) and I was reminded of it again as Arkhan the Black and Neferata and Lamashizzar and others worked to try and recreate Nagash's experiments on the Elixir of Life—which is really, of course, the elixir of undeath/vampirism, not life.
These powerful memes and conventions have their place in fantasy, especially darker fantasy with a more sword & sorcery and/or horror feel, than they do with a high fantasy feel, but even high fantasy, of course, has characters like the Ringwraiths who fill a similar function, etc.