Centaurs encountered in the Core Region and Mojave Wasteland were created by the Master. The creation process involved tossing a varied mix of humans, dogs, and other types of animals into a Forced Evolutionary Virus (FEV) vat to be infected by the virus, and then seeing what mutant chimera emerged as the virus produced rapid and unpredictable mutations. The resultant centaurs can differ quite radically in physical appearance from one another. However, all known centaurs are somewhat humanoid in appearance.
Unlike its two-headed cousins in the Core Region, in this type of centaur only the human-like head and torso remain, and the spines on the back are replaced by 3 long, tentacle-like tongues. This variant of centaur also has a ranged attack: a high-arcing, slow-moving saliva projectile that carries lethal doses of radiation. Strangely, it is also capable of igniting lingering gas vapors as well.
In close quarters, it utilizes its tongue to whip at any intruders. Though it doesn't cause much physical damage, it inflicts a notable amount of radiation damage.
Individual centaurs don't really pose much of a threat to players, but as a rule of thumb, centaurs never travel alone and are usually found with other centaur variants or super mutants. All centaurs are hostile to the player, and when encountered will "spit" slow-moving projectiles at the player in high arcs. They don't do much damage, but increase the player's radiation level dramatically. As the projectiles are slow-moving, however, they can easily be dodged.
In close combat, centaurs do low to moderate damage depending on which type of centaur, but strike very slowly using their tongues in close combat. They can easily be avoided though, as they are very slow moving.
They are not encountered as often as in Fallout 3.
The most common variant found in the wastelands, the centaur on its own can prove very little threat due to its slow speed. However, being the more commonly found variant it is not often encountered on its own. Some can be found near Black Mountain, Jack Rabbit Springs and a large group of them reside in The Devil's Throat, east of Bitter Springs.
As the name suggests, they are a bigger and stronger variant of a centaur. Having been exposed to a higher degree of radiation than regular centaurs, they have significantly more muscle mass as well as thick clusters of tumors growing from their backs.
Though they are slow, they are much tougher and inflict more damage with their toxic spit and whipping tongues than regular centaurs, and are often accompanied by several other centaurs or super mutants. Many centaurs can be found east of Bitter Springs in The Devil's Throat.
An even bigger variety of the evolved centaur, the giant evolved centaur is the largest and most dangerous variation of centaur. They are often surrounded by several evolved centaurs and in rare cases, a super mutant master.
Only one giant evolved centaur can be found, and it is located in The Devil's Throat. This creature normally re-spawns 3 days after being killed, as do the other centaurs found there.
There is a named centaur called Moe who is believed to be Tabitha's pet. Interestingly, Moe respawns if killed. He appears at Black Mountain and is mentioned on Black Mountain Radio in which Tabitha asks her robot Rhonda what her "favorite" centaur Moe is doing (killing him will not frenzy Tabitha, however). Moe can be found guarding two dead Brotherhood of Steel Paladins at the bottom of a highly irradiated crater.
In Fallout 3 they are allied with the super mutants, and it is also possible that they may be allied with them in Fallout: New Vegas, since there is a large group of them in between the Hidden Valley bunker and Black Mountain. In fact, if you do the Still in the Dark quest (the part where you have to find the holotapes) you will find these creatures guarding dead Paladins, which have a holotape on them. Sometimes a super mutant will be in the Devil's Throat, near the truck. On Black Mountain Radio, Tabitha talks about super mutants keeping centaurs as pets, and their perception of humans as prey.