We are the preservers of the balance, now and forever, as Malfurion lies in the Dreaming. Never forget this. - Kal of Dolanaar
Druids are keepers of the world who walk the path of nature, following the wisdom of the Ancients and Cenarius, healing and nurturing the world. To a druid, nature is a delicate balance of actions, in which even the smallest imbalance can create storming turmoil from peaceful skies. Druids draw their power from this wild energy, using it to change their shapes and command the forces of nature. Traditionally druids chose the path of a specific animal totem. Since the invasion of the Burning Legion, however, most druids have undergone a number of reforms, including encouraging the study of magic from all totems. Druids who do this are known as Druids of the wild.
According to Tauren lore, Cenarius instructed them first in druidism as recounted in their myth Forestlord and the First Druids. The series of Warcraft games has not expanded on this hypothesis however. As it currently stands the only in-game canonical record of the "first" druid seems to be that of Malfurion Stormrage whose claim as the first mortal Druid and Cenarius's greatest student; has yet to be challenged.
He would lead the night elves through the War of the Ancients and the long years that followed. With the creation of the World Tree Nordrassil, the Kaldorei druids were bound to Ysera, and her realm, the Emerald Dream, in which they spent centuries of their immortal lives. The Cenarion Circle was formed as the governing society of druids, based in sacred Moonglade.
Locked in slumber in their barrow dens for generations, the druids awoke to meet the threat of the Burning Legion during its recent invasion. After Archimonde's defeat, the druids chose to remain in the waking world and help to rebuild their shattered lands. The Legion's attack left a terrible scar on the natural order, and the druids seek to heal it.
The night elf druids were recently joined in the Cenarion Circle by the Tauren druids. It is not clear from current game content if the Tauren learned druidism separately from the Night Elves or if they were taught by the Night Elves. Conflicting information in the Warcraft universe further exacerbates the confusion. Either way, the Tauren and the Night Elf Druids do not participate in the Alliance/Horde conflict and coexist peacefully within the Cenarion Circle.
Cenarius is the patron entity of all druids. However, each group of druids has its own special patrons and some even have the ability to transform into a being that looks like their patron. Many druids will take on an animal companion based on their patron.