Ancient Barbarian Tribe

The Ancient Barbarian Tribe is a tribe mentioned in The Legend of Zelda: Breath of the Wild. It was barbaric warlike tribe that once inhabited the Faron region of Hyrule in the distant past.

Overview
Little is known about the Ancient Barbarian Tribe, though what is known is that the Barbarian Helm, Barbarian Armor, and Barbarian Leg Wraps is an Armor set created and worn by the tribe and the only confirmed relics of the tribe's existence. The descriptions of the "Barbarian" armor set reveal that the tribe lived in the Faron region, implying they are responsible for the ancient ruins found in the forest and jungles of Faron such as the Zonai Ruins. The tribe apparently no longer exists in Hyrule and its absence is left unexplained.

At some point the Barbarian Helm, Barbarian Armor, and Barbarian Leg Wraps created by the tribe came into the possession of the Sheikah Monk. The Barbarian Helm fell into the possession of Tu Ka'loh and was placed within the Tu Ka'loh Shrine. Dila Maag came into possession of the Barbarian Armor and was placed with the Dila Maag Shrine. Qaza Tokki came into possession of the Barbarian Leg Wraps and they were placed in the Qaza Tokki Shrine. Another surviving pair of Barbarian Leg Wraps came into the possession of Granté who sells them at his Rare Armor Shop in Tarrey Town.

Armor Set
The Barbarian Armor set has a strong tribal theme as it is apparently made from animal hides, bones, and adds tribal tattoos and war paint to Link's skin when worn. The pieces of the armor set are designed to boost the wearer's fighting spirit, battle prowess, and awaken their inner animal to increase attack power, which fits the tribe's apparent warlike nature. When upgraded to Level 2 or higher the set grants Charge Attack Stamina Up which reduces the amount of stamina used by Charged Attacks.

Ancient Ones
One possibility is that the Ancient Barbarian Tribe are actually the Ancient Ones spoken by the Happy Mask Salesman in Majora's Mask who were supposedly responsible for the creation of Majora's Mask which were used by the ancient ones in its hexing rituals before they were forced to seal it away due to the mask's destructive nature. Given the tribe's warlike nature and Majora's Mask resembling the type of mask that would be worn by a tribal witch doctor or shaman, had used the mask to hex the tribes enemies in times of war. It should be noted that the Barbarian Armor set is designed to empower its wearer to increase their attack power and fighting spirit, similar to how Majora's Mask grants its wearer powerful magical abilities. It is possible that the tribe's war-like nature and potentially barbaric the rituals it was used in transformed Majora's Mask, thus explaining the mask's destructive personality. Another possibility is the mask was the cause of their warlike behavior. Presumably the tribe was mostly destroyed by Majora's Mask before the survivors managed to seal it away. It is also possible that after sealing it away, the Ancient Ones experience with the mask's evil caused them to give up their warlike ways and eventually became integrated with the rest of Hyrule.

Interlopers/Twili
Another possibility is the tribe was or later became the Interlopers mentioned in Twilight Princess. Given the tribe's warlike nature, it is possible that the tribe or their descendants may have become involved in the Hyrulean Civil War and after learning of the existence of the Triforce planned to conquer the Sacred Realm with the magic of the Fused Shadow, but were defeated and imprisoned in the Twilight Realm eventually evolving into the Twili, which would explain why the tribe has apparently disappeared from Hyrule.

Sheikah
As the tribe's barbarian armor is found in the possession of several Sheikah (the Monks and Granté), it is possible that the tribe were the early ancestors of or a ancient Sheikah clan/sect (like the modern Yiga Clan) that lived in the Faron region. This would explain why the Sheikah possess artifacts of the ancient tribe which they may have preserved to serve as a reminder of the Sheikah's barbaric past. Another possibly is that the armor set are heirlooms and/or cultural relics. Of course, it should be noted that the tribe is never referred to as Sheikah which is odd considering the Sheikah's prevalence and important role in the story of Breath of the Wild. Another possibly is that Sheikah may have simply preserved the armor as relics of this lost tribe.

Skyloft-born Hylians
As the Barbarian Armor fits Link perfectly, another possibility is that the tribe were Hylian settlers who left The Sky to resettle on The Surface and/or early descendants of the Link and Zelda from Skyward Sword who may have settled in Faron Woods near the Sealed Temple after the defeat of Demise and Ghirahim. The tribe's warlike nature may have been a result of living in Faron Woods which was home to bands of Bokoblins and Moblins as well as other dangerous monsters who the Hylian settlers likely came in conflict with causing the Hylians to develop a warlike culture and may have caused them to become more barbaric as time went on (or they simply seem that way to the modern day Hyruleans who may fail to understand that it was a reaction to the times in which they lived and their new environment). Presumably as conditions got better and the settlers ventured further into Hyrule, the tribe either simply died out and/or those that clung on the their traditions eventually became integrated with the rest of Hyrule at some point, leaving behind only scant evidence of their existence.