Well boy did that come to pass eh? For those who don't know, Nagash is an undead sorcer from the Warhammer Fantasy setting. At the end of 2014, Games Workshop started the 'End Times' and did a lot of different things to the Warhammer Fantasy setting. The first book of that was with Nagash.
But why is Nagash so awesome? I'm approaching him not only from a miniature appreciation, but because it's Warhammer and I've been a player of the Warhammer setting for years, also as a role playing character.
1. The God That Walks: Dungeons and Dragons has a fat bloated goat headed demon lord known as Orcus. Nagash is a man who pulled himself up into a god like status and fought Sigmar, another former man, now god, in hand to hand combat. Fat goat demon versus man who pulled himself into the higher reaches of possible power?
3. The First: Nagash has a lot of things attributed directly to him or about him ranging from necromancy and vampires to lichdom. And if not him creating them directly, him being involved either as a counter against his power or early experimentation. This is one of the few times where a setting has a definitive answer. "Where did vampires come from? Where did liches come from? Where did necromancy come from?"
4. Potent Characters: How can you not love Nagash when he has a follower like Arkhan The Black? I have the original model of this character and he's a lich on a skeleton chariot. His never version is even more impressive. When you need a high priest for the undead? Having someone who might be a match for Vecna when Vecan was a lich as opposed to the deity he became? And how about those on the edges of Nagash lore like Krell, a former Chaos Champion who was raised by Nagash and wound up serving Heinrich Kemmler, the Lichemaster? Those names in and of themselves were of powerful entities and they're just entities on the chain of Nagash's influence.
5. Backstory: Because he wasn't overused, Nagash remained a potent character despite having a terrible model in the older edition of the game. This allowed the writers of the Warhammer Fantasy setting to fire with both barrels and deliver a ton of new models, new characters, new scenarios, and new events that could fit in with what we know of Nagash. In Spartacus, there is rumors of "The Shadow of Death" before Spartacus fights the gladiator. Putting bits and pieces of lore about Nagash well before the characters ever meet him? Classic!
When you want to build a monster of your own for your campaign, you could do far worse than look at how Games Workshop handled Nagash.