Druid

Originally druids were of the celtic priesthood. Of whom little is known, and most of that from the pens of their enemies. This, for centuries, has made them convenient for imaginary priesthoods, ranging from wise and patriotic resisters to Roman conquest, to bloodthirsty practioners of Human Sacrifice.

In modern days, this word is used for a nature-themed spellcaster that usually has flavour of priesthood. Commonly associated powers include:
 * animal empathy
 * speaking with animals and plants
 * speaking with nature spirits (feyfolk, place spirits and so on)
 * Herbology (including making of poisons and augmenting potions)
 * healing (opposite - disease creation - is well known as well, but usually reserved for 'corrupted' cult members)
 * weather manipulation (lightning, winds, rains and so on)
 * Voluntary Shapeshifting
 * body modification magic
 * sometimes overpowered druids can call earthquakes, hurricanes, tsunamies and other innatural natural hazards.

Unlike classical priests and mages, druids have nothing to deal with dead and undead, demons and angels: their power roots in living things, including humans. Druids are usually associated with forests, but other versions are known.

Common associated personality traits are
 * so-called "Practicing Darwinism", better known as eugenics, which is anything but Darwinist (for Grimdark or Corrupt Church versions mostly)
 * Enviromentalism
 * Unlike other fantasy priesthood tropes, druids may worship no specific diety, but unpersonified "Mother Nature" instead. The Sun and/or the Moon are also popular for this.

Compare Witch Doctor.

Literature

 * The main character of the Iron Druid Chronicles is an druid who gets his powers through a bond with the Earth and its many aspects. He can talk to animals and can shapeshift into four animal forms. He can use his magic to imbue herbal potions with extra powers culminating in his Immortali-Tea which keeps him young and immortal. His powers are constrained by a very specific form of Thou Shalt Not Kill which will kill him if he uses his magic to hurt another living thing. As a side result he can only use his magic to heal himself since healing others might be considered hurting their bodies. However, these druids are not pacifists and instead use their magic in indirect ways to make them major Badasses even among the fierce Celtic warriors of ancient Ireland and Scotland.
 * Druids are very prominent in the Shannara books by Terry Brooks.
 * In Simon R. Green's Secret Histories, the Drood family name is the result of linguistic drift from their ancestors being the original druids.

Live Action TV

 * The Druids are a big part of Merlin. They have been persecuted by Uther, helped Morgana with her nightmares, produced Mordred and Freya (who becomes the Lady of the Lake), guarded the Cup of Life, and Merlin, known to them as Emrys, is a big figure to them.

Tabletop Games

 * Dungeons and Dragons has a character class named "Druid", and is likely the base from which all (MMO)RPG druid classes are spawned.
 * A type of creature in Magic the Gathering. Most of them cost green mana, the magic associated with nature, and they often have abilities in some way related to producing mana.

Video Games

 * Diablo II : Lord of Destruction features Druid character class
 * Baldurs Gate series both contain druids and allow you to take one as main character.
 * Druids in World of Warcraft, originally just the tauren (Horde) or the night elves (Alliance), has now spread to the resident werewolves (Worgen, Alliance) and trolls (Horde). It's a bit weird considering that a werewolf would become a cat (and bear) rather than, you know, a wolf, but there you go...
 * Magicka has druids allied with the Beastmen. They only cast spells assosiated with nature in some way, and have the special ability to summon treeants.
 * Battle for Wesnoth includes druids as an advanced spellcaster for the elves. They can entangle units and have a magical attack.
 * Fall From Heaven includes druids as advanced priest units with additional nature spells.
 * Might and Magic's Druids have varied between game and game, from Heroes 1 and 2's energy-bolt throwing guys in hooded robes, to Heroes 3's Magic Hero for the more nature-themed castle, over Might and Magic VI and VII's generalist spellcasters.
 * King's Quest VI had an island of Druids.
 * In the Dragon Age series, many apostate mages who live outside the Chantry seem to fall into this category.
 * Morrigan from Origins, Velanna from Awakening and Merrill from Dragon Age 2 all are variations on this role. The former being one of the legendary Witches of the Wilds, while the latter two were both trained as Dalish Keepers.

Web Original

 * The Questport Chronicles: A pair of druids named Acre and Jaheira help out the heroes from time to time.