Maragor is the land of an extinct people called the Marags. It occupies a fertile area to the east of Tolnedra, well fed with multiple streams that also washed many valuable minerals - including gold - down from the bordering mountains.
The Marags were the children of the God Mara. Seeking to take for themselves the large amounts of gold that existed in the streams and rivers of Maragor, the legions of Tolnedra swept in to Maragor and wiped out the Marags. Mara remained in the ruins of Maragor's capital, Mar Amon, mourning his lost children and protecting the ruins of Maragor from gold hunters, until the descendent of a Marag taken as a slave by the Murgos named Taiba and her Ulgo husband Relg moved back to Maragor to regenerate the lost race.
The Marags were often seen as savages by the other races due to their practice of cannibalism. Belgarath points out in Belgarath the Sorcerer that the Marags only cannibalized members of other races, and only did so due to a misreading of Mara's scriptures. He also says that eight out of nine Marags were female. Polgara dislikes the Marags because of their cannibalism as well as because of societal practices deriving from the overwhelmingly female populace (in particular, polygamy seems to have been practiced).
By the time of The Belgariad, Maragor is a haunted place, filled with the shades of the dead, spectral ghosts with no corporeal substance but whose appearance frightens passersby to the point of insanity. Though Maragor is still rich in gold, the only living creatures to pass inside the boundaries of the country are the "Mad Monks" of Mar Terrin, a group of Tolnedran holy men who attempt to minister to the ghosts and to those whom they have made mad. Belgarath refers to them as "Toldnedra's conscience" when he sees a group of them, referring to the small segment of Tolnedra which feels guilt at the genocide committed in Maragor.