Centaur

Centaurs are misshapen, mutated creatures. They are a by-product of the Forced Evolutionary Virus, as they were created by tossing a varied mix of humans, dogs, cats, brahmin and other animals into an FEV vat and seeing what came out the other end. As a result, they can differ quite a lot from one another.

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

West Coast
In the Core Region, centaurs 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 the back for 3 long, tentacle like tongues. Unlike its core region 'cousins', the Capital Wasteland Centaur uses a ranged attack: a high-arcing, slow-moving projectile that can carry lethal doses of radiation. Oddly enough, it is capable of igniting lingering gas vapors as well, indicating some kind of pyrophoric quality as well. Centaurs are known to accompany Super Mutants as "guard dogs," so if you see one, expect super mutants ahead.

Fallout 3
Centaurs will pose a moderate danger to low level players but they're moving so slowly and having long, tentacle-like tongues which can be targeted in V.A.T.S. makes them easy to deal with. They sometimes carry chems like Jet. A good idea is to move out of the way when it spits at you which is fairly easy. Centaurs are generally not alone, if you are attacked by one there is a moderate chance it will be accompanied by a Super Mutant or a Super Mutant Brute although it is not always the case, it often can be.

A good strategy when fighting with Centaurs is to snipe one at medium range. Even then, a player can easily side-step at the moment when the Centaur throws a slimy radiated substance at him. Any decent middle-ranged weapon like the Assault Rifle or 10mm SMG will do the job. Targeting in V.A.T.S. for a Centaur's tongue may be tempting but due to its small size it is often a waste of ammo. Shooting in the head is a more effective solution. It is much bigger than the tongue and few rounds from mentioned weapons is enough to kill it. If the opponent manages to survive through the first V.A.T.S. sequence, just side-step his shot and attack again.

It should also be noted that, contrary to popular belief, the centaur actually has the highest Perception stat of any enemy in Fallout 3, at 9, meaning that Centaurs can often detect the player before the player can detect them.

Appearances
Centaurs appear in Fallout, Fallout 2 and Fallout 3.