Some of the classes of warcraft were added with expansions and some were originally there.
NOTE: There are thirteen classes in total.
Warriors are the most honored men and women of the alliance and horde being able to rush into battle and withstand the unrelenting punches.
Warlocks are fierce ranged combat specialists, enlisting the aid of demons and shadow magic to destroy their foes.
Ranged attackers who enlist their pets and bows to destroy their foes from beyond.
Added in the mists of pandaria expansion.
Martial arts masters who destroy with swift strikes and use their calm and focus to attack.
Masters of magic, they use arcane magic to beset their foes.
Friends of the elements, they employ nature magics and totems to defeat their enemies.
Masters of assassination, these daredevils prefer to stay in the shadows, work from the shadows, and kill from the shadows.
Users of the holy light, these are warriors of the light. They use light magic to destroy their enemies, and believe the light will purge all evil doers from the world.
Healers and users of the light, these people believe that where there is darkness, there is always light.
The following three classes are hero classes, meaning they have special start zones and start at a higher level (usually level 10.). All of them were added in a expansion.
Added in the wrath of the lich king expansion
Harnessers of death magic, they were created to be used as soldiers of the scourge but broke free from the lich kings control and allied with the alliance and horde to destroy the lich king. After the lich king's death. They renamed themselves, the knights of the ebon blade.
available to: All races except for dracthyr
Elves who follow illadan stormrages path. They will not stop until the legion has been brought to its knees.
Available to: Night elves and blood elves
Masters of the dragonflight magic, the dracthyr were created by neltharian and put into a deep slumber. Now they have awakened, and have allied with the alliance and horde to venture to the dragon isles.
Available to: dracthyr only