They are an independent race of desert nomads who roam the desert, free of Arridi control. However, though they are certainly powerful, they rarely fight. They entered into an alliance with the Arridi to defeat the Tualaghi, a tribe of nomads who specialize in quick, merciless raids.
A Bedullin tribe in Erak's Ransom, the Koresh Bedullin, find Will lost in the desert and close to death. They nurse him back to health and help Will defeat the Tualaghi because they feel guilty, having accidentally led the Tualaghi to capture the party Will was originally with. They found Tug wandering in the desert, and they took him in, claiming that he was theirs due to the law of the desert, which states that if a person releases a horse, and someone else finds the horse, the animal then belongs to the finder.
They are all avid gamblers but do not mind loosing. Gambling is said to be something close to a religion for the Bedullin, and this avid love of gambling is how Will wins Tug back, by racing him against the Koresh Bedullin's best horse and winning.
The Koresh Bedullin play a part in the final battle of Erak's Ransom, helping Selethen, Halt, and their party not only escape the Tualaghi, but also effectively decimate the Tualaghi, and possibly even eradicating them altogether.