Very, very few classes or class concepts have been gone over more than the Necromancer. For a class that was never part of the original game, and never actually a proper class in it's own right, a lot of ink and pixels have been spent on this class. So much that I am sure to miss things and might even need a part 2. Where do we start?
Taken from the Greek a necromancer is someone that communes with the dead. So spells like Speak to Dead are a good example. Historical necromancers, like for example John Dee, spoke to the dead to get advice. or foretell the future. In modern parlance and certainly in games (maybe one caused the other) necromancy has come to mean a wizard that controls or manipulates the forces of death and unlife.
The easiest Necromancer is simple. Play a Wizard/Magic-User and then only choose necromancy spells. Wear a lot of black and hang out with undead. This is also a very satisfying necromancer since all the trappings have to be role-played. Alternately one could play a cleric of a god of death, take only reversed necromancy spells and command instead of turn undead.
I think though as time wore on people wanted something that wa little bit of both.
The first, or at least one of the first was from White Dwarf Magazine #22 from December 1980/January 1981. Lew Pulsipher gives us an article about evil priests, the "Black Priests". While these are more cultist, there is a lot of necromancy being thrown around. This is followed by a true necromancer class also by Pulsipher in issue #35 from November 1982. Either of these classes is fine and represent the design philosophy of the times. Namely take and rearrange already familiar elements. The Black Priest and this Necromancer have the same shortcomings though; a reliance of human sacrifice.
The Necromancer is turned up to 11 with the publication of Dragon #76 in August 1983 and Len Lakofka's death master class. Designed to be an "NPC Class only" I remember seeing it first in the pages of Best of Dragon Magazine Vol. 3. I admit, I rolled up a death master right away. He became a major antagonist in my games for many years to come.
In AD&D1 the example of the Illusionist gave birth to the speciality wizards of 2nd Ed. One of those speciality wizards was the Necromancer. This continues in practice to the most current version. Though unlike the Illusionist, the Transmuter or even the Evoker, the Necromancer got it's own book. The Complete Book of Necromancers was one of those books that everyone seemed to want. I remember picking it up back when it was first published. I paid $15 for it. Later the cover price jumped to $18 and soon it became very rare. No idea why. The aftermarket price jumped considerably and I ended up selling mine on eBay back in 2000 for $81. Not a bad deal really. I recently picked up a copy at Half-Price Books for $9. The PDF just about the same price. Though the book is crammed full of necromancer goodies. Spells, magic items, undead familiars.
Moving out into the world of Fantasy Heartbreakers there is the near-compatible Quest of the Ancients. This necromancer reads like the Death Master, but has some interesting spells and some powers. The Arcanum/Bard Games also has a necromancer class.
3.x had, at the last time I looked, at least 3 different kinds of official Necromancer classes. The two best are from Libris Mortis: The Book of Undead and Heroes of Horror. Heroes of Horror featured the rather popular Dread Necromancer class. There is also the Death Master class from Dragon updated to 3.0e. The Crypt Lord from the aptly named Necromancer Games. Not to mention dozens of others from other third party publishers. Most take the same elements and reorganize them, but every so often something new is produced.
4e had necromancers as well. It was a type of wizard (much like the witch was) and was introduced in the Player's Option: Heroes of Shadow book. It had some rather neat features to it as well.
For the OSR things are really no different, dozens of different types and sorts of necromancers. I am only going to talk about a few.
One of the simplest also belongs to one of the simplest OSR games. Basic Fantasy has a necromancer class on their downloads page for free. It has a lot of spells and weighs in at an appropriate 13 pages.
I would have to say one of my favorites, at least in terms of style, is the one from Astonishing Swordsmen & Sorcerers of Hyperborea. The necromancer here is cut from the "evil cultist" mold like their warlock and has a lot of great spells and powers.
Magical Theorems & Dark Pacts also has a great necromancer and the big feature of this class (and this book) is the number of spells. While this book as more spells, the AS&SH class is slightly better in terms of what I want. Right along with that is the necromancer from the great Theorems & Thaumaturgy. A basic class, but some really nice spells.
Another really cool one in terms of how the necromancer is presented is the one from Adventures Dark & Deep. Darker Paths 1: The Necromancer is certainly in the vein of the "this is an evil class" but +Joseph Bloch makes no bones about the fact that players will be playing these as evil characters. It's sort of the point of his "Darker Paths" series. In that respect this is a good one to pick up just to get some ideas on how to play an evil character. Plus it has some unique spells.
Back at home I have most of these printed out and put into a folder. I also have a number of character sheets of all the different types of necromancers. Basically I have six characters with two sheets each; a 3.x sheet and an OSR compatible one (the five above and an old fashioned MU with necromancy spells). This gives me 12 different sorts of necromancers for 6 characters. I call them the Order of Six based on a group I introduced in my Buffy games. I am planning on using them as my bad guys in my games, but right now I am only playing 5e! So I can't really judge how well they all work. Similar to what I did with the Witch's Nest. Sounds like a plan to me.
By the way. My son has a 5e game he is in charge of. He has a 15th level necromancer in that game and it is wicked.
I feel like there is alot more to say but I have only scratched the surface.
What is your favorite necromancer class?