They nearly wiped out the tauren. What they lack in brains, hygiene or manners they make up for with raw, bestial aggression, riding in herd-like tribes to try and dominate the land they themselves metaphorically descend from. Born from the union of earth elemental and spirit of nature, they descend from Therazane and Cenarius, and yet it is fair to say that at best, the apple has fallen from the tree and rolled some distance from these ancestors. Their presence in Azeroth often befouls, as they seem to see no need to take care of the land they themselves descend from, for they are not grateful children. Their father Zaetar died at their hands.
They are the centaur. Before the coming of the Horde, they were the most likely to rule The Barrens, what is now Durotar, even Desolace. The past 10 years have seen their numbers fall, their power fade, pushed aside by the tauren and their new allies, but they have not faded away yet. From their fortress of Maraudon, they paradoxically guard and watch over the site of their father's grave, the crystal caverns of Terramok where their mother, Princess Theradras, was sealed away by the Titans.
Born of a forbidden union, cursed by patricide, the centaur abide.
A death in the family
The centaur were born from the love of Princess Theradras, daughter of Therazane the Stonemother, first among earth elementals, and Zaetar, son of Cenarius. How these two met is a mystery. Theradras seems to have sincerely loved Zaetar to the point that she tells Cho'gall himself that she will not leave Terramok, even though it long since lost the power to hold her confined simply because it contains Zaetar's remains. However, apparently in death, Zaetar's spirit has had time to think over his liaison with Theradras and has come to the conclusion that it was a mistake. If you've been leveling an alt recently through Maraudon, it is now the spirit of Zaetar who gives the quest to strike down his former love.
Of course, Zaetar was put to death by the children he sired upon her, so it's possible he's bitter.
There are conflicting rumors as to the origins of the centaur tribes. While the story of Zaetar and Theradras is manifestly true for the five large centaur tribes of Desolace, their former stronghold, some argue that other centaur descend from another son of Cenarius known as "The Centaur" and that there were three children of Cenarius: the centaur, the dryad, and the keeper of the grove. The problem with this theory is that we've met at least two of Cenarius' children so far, Remulos and Zaetar, and both are of the keeper of the grove type, effectively identical to their father. It's possible and perhaps even likely that over time, Zaetar's story was twisted and changed to fit the role of the mythical "Centaur" -- but as yet, we don't know for sure, and there's nothing in game that says that Cenarius only has the two sons.
The Horde breaks the back of the advance
If not for the coming of the orcs to Kalimdor, the centaur tribes would almost certainly have wiped out the nomadic tauren. While tauren are massive, skilled hunters and warriors the centaur are actually larger (some weighing nearly as much as two tons) and have their own mounts built in, being even faster and far more aggressive. While a tauren likes to only reside in an area as long as he or she can do so without upsetting the local balance, centaurs gleefully use up an area and then move on to a new place to destroy. It was the aggressive, destructive aspects of the centaur that moved them to wage war on the tauren, not the other way around; as fecund as they are, it did not particularly bother them to use five or six for every tauren they killed, since they were happy to breed more.
In fact, this state of affairs also exists between the various centaur tribes. Centaur shamans, usually female, wrestle the elementals into submission (much as the Taunka of Northrend do), while the males simply beat each other to death. When two tribes meet, there is almost always bloodshed. A figure known as the Centaur Pariah once attempted to recruit outsiders to help him unite the tribes of Desolace, but following the Shattering of the world, he has fallen silent. Amazingly, his quest to unite the centaur of Desolace involved the ghosts of the five khans who themselves killed Zaetar and founded the five tribes.
As things stand, the descendants of Theradras and Zaetar actually find some of that unity spoken of by the Pariah following the Shattering of Azeroth. The centaur tribes of Desolace are unified in opposition to the Burning Legion and their servants. Ironically, part of the reason for this change of heart on the part of the centaur is the work of tauren druids in the new Cenarion Wildlands, a blooming place of reviving nature in the heart of Desolace itself. It's a minor irony that a tauren could help unite the centaur.
We know from events during the Third War that there were once centaur tribes in the Eastern Kingdoms serving as mercenaries for the armed forces of other races. At some point, based on the amount of centaur skins inside the Dark Horde's fortress at Blackrock Mountain, they must have come into conflict with the orcs and may have been wiped out. For certain, there has been no sign of them in the years since the Third War. We don't know if these centaur were related to the ones of Kalimdor directly or somehow came into being via another source. They would have been as cut off from their ancestors as the high elves of Silvermoon were, of course.
In the end, the centaur have indeed been driven back to the point of near extinction by the Horde yet may have found unity through their adversity and the actions of outsiders in rekindling the life of their home base of Desolace. Will we see a new centaur nation rise? Will it be destructive and chaotic (as befits the children of Theradras, servant to the Old Gods), or will it seek to reach out a hand in peace for once in their existence as the sons and daughters of Zaetar, the grandchildren of Cenarius, might? Only time will tell.
While you don't need to have played the previous Warcraft games to enjoy World of Warcraft, a little history goes a long way toward making the game a lot more fun. Dig into even more of the lore and history behind the World of Warcraft in WoW Insider's Guide to Warcraft Lore.