The Horde race that starts in Mulgore is the tauren. Mulgore is the broad, grassland homeland of the tauren in central Kalimdor, and newly created tauren characters traditionally begin their early quests there.
The tauren are large, bovine-inspired people whose culture emphasizes the Earth Mother, reverence for nature, ancestral traditions, and the spiritual leadership of their shu’halo elders. Their capital, Thunder Bluff, stands on enormous mesas in Mulgore and serves as the race’s political and cultural center.
The race joined the Horde after Orcish warchief Thrall helped Cairne Bloodhoof defend the tauren from the centaur. That alliance explains why tauren are a Horde race, despite their close ties to the land and their generally peaceful reputation. The other options begin elsewhere: orcs in Durotar, trolls traditionally in the Echo Isles or nearby Durotar, and undead in Tirisfal Glades.