Preserver

Preservers are a Variant Class (technically) of Wizards from the Dungeons & Dragons setting of Dark Sun. The benevolent counterpart of Defilers, whilst Preservers also draw power from the lifeforce of Athas (or from the Cerulean Storm, or the Black, or the Gray), they do so slowly and carefully, making sure to only take what they need and working their magic in such a way that the energy left over will feed back into the planet when they cast the spell. Unfortunately, because defilers are so well-known, preservers are regarded with just as much hatred and fear.

In Advanced Dungeons & Dragons, Preservers and Defilers were treated as entirely separate classes. Preservers used all the normal rules for wizards and could even become specialist wizards, at least until the Revised Edition of the campaign setting retconned that there were no specialist wizards on Athas due to the long persecution of wizards. Even in the revised edition, Preservers were defined by functioning like normal wizards, whilst defilers gained levels faster but exposed themselves to danger through the destructive after-effects of their spellcasting and had their ability to successfully prepare spells tied to a randomized table mechanic. The splatbook "Defilers and Preservers" further molded the difference by presenting new rules for associated spells, with Preservers having a +15% chance to learn Abjurer and Diviner spells, but a -15% chance to learn Conjurer and Necromancer spells (Defilers were the opposite way around) and presented complicated rules for switching from Preserver to Defiler or vice versa in game-play, inspired by the Prism Pentad, in which a preserver protagonist succumbs to desperation and defiles more than once.

This inspired the future treatment of Preservers and Defilers. In both Dungeons & Dragons 3rd Edition and Dungeons & Dragons 4th Edition, Preservers are still the "normal wizard" type class, and defiling is presented as more of a temptation that preservers face; a "defiler" in the AD&D sense of the term is essentially a wizard who routinely uses the edge that defiling gives them, whilst a preserver avoids it until and unless they feel they have no choice.