In World of Warcraft, Night Elves, Tauren, Worgen, and Trolls can become druids. They are spell casters (healer/damage dealer hybrids) in their humanoid form, but they gain the ability to shapeshift into different forms as they progress through the game. The basic forms that every druid can have, sorted by the order they become available, are: Cat, Bear, Travel (cheetah/stag), Aquatic (sea lion), Stormcrow and Swift Stormcrow. Depending on how a player distributes their talent points two additional forms may become available: Moonkin and Tree of Life. The forms let druids assume a specific role in a group or they provide utility functions such as improving travel speed. They have spells that seem to be very close to nature in their name and function, like Regrowth, Tranquility, Typhoon, Barkskin or Eclipse. In their feral forms they have ferociously sounding abilities that resemble animal actions like Prowl, Bash, Pounce or Growl.
Druids take less damage and appear to be more threatening to monsters while in Bear form, and they can use relatively low damage but high threat physical abilities like Maul or Lacerate, or they can Swipe multiple targets to generate threat on all of them, making Bears suitable for tanking. Cat form is the opposite, but also builds on physical damage abilities, with gameplay mechanics similar to that of rogues, including stealth and alternatives for most of their offensive moves; Cats excel in damage dealing so in cat form the druid assumes the melee damage dealer role. The travel and Cheetah forms gives extra running speed so it is useful for escaping or traveling. The Aquatic form is the same except that it's only usable while underwater, but it provides both extra swimming speed and unlimited breath. The Stormcrow and Swift Stormcrow (or Flight Form and Swift Flight Form) gives the druid the ability to fly at the same speed as that of the level-appropriate flying mounts in the game, with the same restrictions of course. The druids specialized in Balance can shapeshift into a Moonkin, which will enhance the druid's and their group's offensive spells, making them viable as ranged damage dealers and support. Finally, Restoration druids can temporarily assume Tree of Life form, which boosts the strength of their healing spells, their armor, and empowers several of their abilities while they are in the Tree of Life form.
One unique feature of druids in PvP combat is that in their different forms (except normal humanoid form) they are immune to polymorph effects and the act of shapeshifting frees them from any polymorph or movement impairing effect. Another unique feature of druids that is more apparent in PvE combat is that they can resurrect dead group members even in combat, while normal resurrection spells only work out of combat. However, this powerful resurrection spell has a long (10 minutes) cooldown.
Druids are the most versatile class in the game, but they lose their instant versatility already on lower levels, as later on a druid that is specialized in the Restoration talent tree for example will not be able to effectively tank in a high level instance just by shapeshifting into Bear form. However, with the proper talent specialization and equipment a druid can be either a fully viable tank, healer, spell caster or melee damage dealer, just not all of them at once.
As of the recent expansion, Cataclysm, the new Alliance race Worgen and the Horde's Trolls are able to become druids in addition to Tauren and Night Elves.
Read more about this topic: Druid (character Class)