Lich
Liches (from Leiche, German for "corpse") are necromancers who have managed to master their art and straddle the line between life and death. After decades of research, practice, and gathering of materials, a lich-to-be performs a ceremony that extracts the soul from his or her body and places it in a phylactery, usually an ornament of value to the lich. After that, if the lich's body is ever destroyed, it will reform at the phylactery, so long as the phylactery remains intact. This makes them a nice persistent foe for a DM to throw at at a party. Other benefits of lichdom include the ability to live without eating or sleeping, giving the lich that much more time to get things done.
The ceremonies for becoming a lich (and most forms of necromancy, for that matter) tend to involve sacrificing of souls and killing of innocents, so liches are generally of evil alignment, but a person who neither eats nor sleeps and reforms after being destroyed can certainly do a lot of good; depending on the setting, it may be possible to become a lich without doing anything irredeemably evil (or even mean-spirited).
Back in 2e D&D, liches came in multiple types depending on what kind of magic was used to create them. Your common lich was a former wizard, with separate stats in other splats for clerical, bardic and psionic liches.
Lich Variants
Archlich
A lich who took longer to become a lich, and has a diminished spellcasting capacity (some spell-like abilities and 9 spells from their original spellbook) but isn't evil in the trade-off. Introduced in Spelljammer, but mostly ignored by later settings and editions, up until it got to be an Epic Destiny in 4e.
Balenorn
A good-aligned elf lich, created willingly from an elf who wants to be undead only to guard something very important or who wants to stick around beyond death to keep watch over their family.
Death Knight
Essentially the gish version of a lich, an undead warrior-wizard. Originally just the next step up from the skeleton warrior by gaining some increased HD and spell-like abilities, they got more lich-like in 4th edition, complete with their chosen weapons doubling as their phylacteries.
Deathless
A race of goodly lich-like undead created in 3rd edition for the Eberron setting. They're fueled by Positive Energy rather than Negative Energy and are basically "reverse liches".
Demi-Lich
A lich who derped around for so long that his body is just a flying bit of skeleton (usually a skull) full of soul gems. Despite their small size, they're much nastier than a normal lich; their spellcasting is even stronger, they have oodles of opportunities to cast Soul Trap and bone you, and they like to fly juuuust out of players' easy reach. They are also immune to most spells and magical effects, except for a few holy-powered ones and one derpy second-level spell called shatter that screws them something fierce by blowing out their soul gems. Their lore's flipflopped between editions, going from the next step in lichly evolution to a weakened form caused when a lich either gets too bored with existence (Pathfinder), or fails to eat enough souls.
Dracolich
Lichified dragons, mostly associated with the crazy Cult of the Dragon from Forgotten Realms who want to create dracoliches to rule the world. They still have phylacteries, but need to possess a dragon's physical remains to come back rather than just regenerating.
Drow
Drow and Driders got their own lichly variants back in Advanced Dungeons & Dragons, due to that ruleset not being able to handle slapping templates on existing creatures.
Dry Lich
Basically a mummy lich, and the ultimate result of the "walker in the waste" prestige class. Can't be good aligned, but doesn't have to be evil aligned either. They also get some cute Con-draining and desiccating attacks liches don't, and five phylacteries in the form of canoptic jars containing their organs, all on top of getting the template for free as part of their advancement.
Fireliches
They come from the Spelljammer setting and are what happens when an idiot wizard undergoing the lich transition ritual casts a fire spell in the Phlogiston... which is, essentially, an entire dimension full of flammable gas. The result is a cursed undead who basically exists as a giant free-floating sapient fireball with a skull in its center. Said skull is perpetually screaming in pain, as their existence is one of endless burning torment from the fire engulfing their very soul. They have the bad habit of crashing into spelljammers like sapient missiles in a futile attempt to end their tortured unlife.
Grey Shivers
Spiders that take up residence inside the skulls of destroyed liches, and absorb fragments of the lich's soul, turning them into sapient, spell-casting monsters. Whilst still being little spiders hiding inside skulls.
Illithiliches
Also known as Alhoons. These are Mind Flayer liches, and the inevitable result of any illithid that chooses to abandon the Elder Brain, as they're all terrified of the idea of ceasing to exist after death.
Inheritor Liches
Hailing from the Birthright setting, they are what happens when one of the local Inheritors turns into a lich.
Master Liches
Another Spelljammer creation, they were turned into liches by pacts with Demon Princes or Arch-Devils, but then betrayed their master and fled into Wildspace to avoid paying their debt. The big difference is that they don't have a phylactery, but have a fairly potent regeneration ability.
Suel Liches
Originally from Greyhawk, they are a sort of lich-wraith hybrid; in their natural state, they're immaterial beings of pure Negative Energy, the twisted souls of wizards slain by the Rain of Colorless Fire, so they possess living hosts to interact with the world around them. But, said body decays at a rapid pace, until eventually it crumbles into nothing and they gotta grab a new one.
Vassalich
A lesser form of lich introduced in the Ravenloft setting - mages who couldn't get the mojo to transform themselves, so they sold themselves as slaves to existing liches and became weaker knock-offs. They can turn into real liches, in time, but it's not easy and their masters keep a tight grip on them.
See Also
- Drew the Lich, a Quest where /tg/ played a lich.
- The Millennial King, a story and setting inspired by /tg/ speculating on what a good necromancer would be like. To make a long story short: he becomes a lich and leads his kingdom to an era of prosperity with a skeleton-powered industrial revolution.
- Deep Rot, a skeletal supercomputer constructed by a mad lich.
- Dreadnought, which, when a Librarian is entombed within, is basically a mecha-lich.
- Nagash, everyone's favourite Warhammer lich.
- The Bank of Liches, what happens when a bunch of liches decide to pool their phylacteries in a safe and secure location.
- Vecna, a god that is a lich.