Bariaurs are a playable race from Planescape, first introduced to the D&D scene back in Advanced Dungeons & Dragons 2nd edition. They were one of the three playable races introduced in A Player's Guide to the Planes, the player's handbook of Planescape, alongside the Githzerai and the Tieflings.
Bariaurs are a planar race hailing from Ysgard, an Upper Plane that lies on the border between the Neutral Good and Chaotic Good planes. They resemble centaurs, though smaller, with the body of a large mountain goat or a bighorn sheep - the books cannot seem to keep which it is straight, because they insist on referring to males as "rams" and females as "ewes", even though they are outright stated as resembling a "goat". Males of the race, and a tiny minority of females, have long curling ram horns growing from their foreheads, which give them a natural weapon attack. They are best known for being very vain, always fussing over their appearance, and for their strong racial wanderlust. Also, despite their obvious resemblance to centaurs, they consider being compared to them insulting.
Bariaurs exhibit sexual dimorphism in their stats, with different ability scores and racial abilities for both genders. Males get +1 Strength and Constitution, -1 Wisdom and Dexterity, the ability to headbutt for 1D8 + Str bonus damage, a charge attack, and the ability to be fighters, rangers, paladins or priests. Females get +1 Wisdom and Intelligence, -1 Strength and Dexterity, +2 bonus to surprise rolls against ambushers that "make noise or have smells", +3 to saving throws vs. spells, and the ability to be fighters, priests or wizards.
Bariaurs have never been very popular amongst the fans; even the Aasimar were more popular, despite not originally being one of the Planescape PC options. They were forgotten about for most of 3.x edition, although they did appear in both the Manual of the Planes and the Book of Exalted Deeds, and had a Creature Class write-up in Dragon Magazine #312. They never made the transition to 4th edition, and have yet to be seen in 5th edition.
There are two semi-official netbooks that expand upon the Bariaur; The Complete Book of Bariaur, which is a huge expansion on their culture, classes, characters, etc, and The Bariaur Book of Belief, which covers bariaur rituals, legends, religious rites and more, serving as a sourcebook for bariaur wizards and clerics. Currently, however, the only place you can find these is on Scribd: