Centaur

Centaurs are misshapen, mutated creatures. They are a by-product of infection by the Forced Evolutionary Virus, and some of them were created by the Master by tossing a varied mix of humans, dogs, and other types of animals into an FEV nutrient vat to be infected by the virus and then see what mutant chimera emerged as the virus produced rapid and unpredictable mutations. As a result, centaurs can differ quite radically in physical appearance from one another.

The centaurs are not only created by the FEV, they also seem to live quite successfully in a heavily irradiated environment.

West Coast
In the Core Region, centaurs were created by the Master and frequently travel in packs with floaters. They encompassed a large bulk of the Master's armies and are commonly found with the nightkin and other remnants of the Master's army who roam Northern California.

Capital Wasteland
The centaurs encountered in the Capital Wasteland are physically different from the centaurs from the Core Region, trading the dog-like head for a human one and the feelers on their back for 3 long, tentacle-like tongues. Like their western counterparts, they are created by infection with the FEV along with the super mutants, so their birthplace is Vault 87. Unlike its Core Region "cousins", the Capital Wasteland centaur uses a ranged attack: a high-arcing, slow-moving saliva projectile that can carry lethal doses of radiation. Oddly enough, it is capable of igniting lingering gas vapors as well, so beware if fighting one in an area with gas leaks. Centaurs are known to accompany super mutants as "guard dogs", so if you see one, expect to find super mutants ahead.

Mojave Wasteland
Centaurs can be found in the Mojave Wasteland in irradiated areas. Far South of new Vegas, and north west of Primm is the Scorpion Gultch (look at the map for what looks like a set of switch backs on the road, its south). go through Scorpion Gultch heading west to east and neat the end there is a large crater that contains a few Evolved centaurs and an Evolved centaur named Moe. In the crader if you brave the radiation you will find 2 dead Brotherhood of Steel soldiers which are wearing T-51b power armor as well as a laser rifle with some ammo.