Necromancer
A Necromancer is a kind of magic-user who practices necromancy. "Necromancy" comes from the Greek words nekros ("dead body") and manteia ("prophecy"), and in its strictest sense, refers to the practice of communing with the spirits of the dead to learn about the future. Over the centuries since the coining of the word, its meaning has broadened to include any kind of magic relating to death and the undead, and thus the necromancer's portfolio has also broadened. Necromancers in more modern works are known to reanimate dead bodies, summon ghosts, and drain life-force from the living to fuel their ceremonies (or themselves). Surprisingly, they aren't generally known for fortune-telling nowadays.
Because death is scary, and in many cultures and religions, tinkering with life and death is reserved for the gods, necromancers are generally perceived as evil, and necromancy sometimes inherently so. A common storyline is that a person with magical talent falls in love, said beloved dies, the magic-user dabbles with necromancy to try to bring him or her back, loses sight of the goal, and before they know it, they're turning people into zombies and hamming it up like Skeletor. Some settings are shifting to a more nuanced approach that acknowledge that necromancy, like any skill, can be used for good or evil, but the majority of necromancers are Neutral Evil.
In settings where the spectrum of this school stretches pretty far, it generally tends to be that benign necromancy-related magic is referred to as "White Necromancy", with nasty undead-raising and life draining fuckery tending to be "Black Necromancy".
Warhammer 40,000
Warhammer 40,000 doesn't have necromancy per se, but the followers of Nurgle can be like necromancers in many ways, especially when they start breaking out the Zombie Plague. Additionally, the way in which spiritseers are able to coax the souls of dead Eldar from the infinity circuits into wraithbone constructs technically makes them necromancers too, albeit of a different sort than the Nurglitch kind mentioned above.
Warhammer Fantasy
Warhammer Fantasy Battle's magic system features the Lore of Death as one of the eight standard schools of magic. Its practitioners tend to be a little gloomier than most, but the forces of Order are plenty willing to make use of them so long as they kill enemies. There are also regular necromancers. Long ago, in the land of Egypt Khemri, there were a bunch of mage-priests who practiced a kind of magic in their rituals to honor the dead. But a mage-priest named Nagash fucked all that up, turning their entire country into undead, and trying to take over the world. Now there are two variants of necromancy, the uncorrupted kind practiced by the Khemrian Tomb Kings, and the regular kind used by necromancers and Vampire Counts.