The original six brothers were a band of six legendary Saradominist warriors who assisted Saradomin in his campaign to conquer southern Forinthry during the God Wars and soon after ventured into Morytania, leading the Morytania Campaign. While they were originally farmers in a small village, they struck a deal with the Zarosian MahjarratSliske to become more powerful on Guthan's advice. Sliske was also responsible for gifting them their iconic equipment.
When they had nearly finished their campaign and were at the borders of the Sanguinesti, Sliske took the power he had gifted back from them, allowed them to weaken, and then "collected" them after their deaths. They were buried in six burial mounds, or barrows, in eastern Morytania, in order to guard a powerful artefact pivotal in the return of Zaros. Even after their deaths and the retrieval of the artefact, they serve Sliske as wights.
Since then, Sliske has collected two additional "brothers": Akrisae the Doomed in Ritual of the Mahjarrat, and Linza the Disgraced in Kindred Spirits. While they do not possess a familial relation to the original six, they are still considered to be part of the Barrows brothers collectively. Unlike the original brothers, they do not have their own tombs, but rather share them with Verac and Ahrim, respectively. They are also not fought during Rise of the Six, and do not have bobblehead pets.
The brothers are summoned by their master Sliske during the 18th Ritual of Rejuvenation. Arriving at the Ritual Plateau, they initially fought off the Armoured Zombies under the control of Zemouregal. After they defeated the zombies along with the player, Sharathteerk under Zemouregal's orders summoned the hero of Varrock, Arrav. In this battle of the undead, Arrav had the upper hand - such was his might that the Barrow wights were unable to harm him. Arrav ceased fighting the brothers after the player distracted and led him to the area where his heart was buried, causing him to break free of Zemouregal's control.
After the ritual, Sliske, having been impressed by the player's prowess, attempted to convert the player into a Barrow wight. His conversion spell was however intercepted by Akrisae; thereafter known as Akrisae the Doomed - the newest of Sliske's Barrow wights.
During the 'Grand Ascendancy' - a gathering of gods arranged by Sliske - the Barrows Brothers and Akrisae were summoned to the Empyrean Citadel to bar access to the meeting chamber from non-divine beings such as Zemouregal, who attempts to force his way through, but is denied by the power of Sliske. Shortly after the meeting, Sliske experimented with the Barrows Brothers in the Shadow Realm, granting them extra powers and some control of it.
History of the brothers is given with greater detail showing that Guthan was the one that convinced the others to accept Sliske's offer. Various secrets with the brothers are revealed, such as Ahrim's relationship with Isolde and Verac's secret worshipping of Zamorak. Dharok represents the brothers after the player leaves with the remaining hostages and thanks them for their assistance, regardless of what they have done and vow to assist them when the time is right.
During this time, Sliske converts Linza into Linza the Disgraced after revealing her betrayal to the player. He originally wanted to convert her after she died, but decided to convert her immediately instead.
The brothers return, having been summoned by Sliske to kill the player after they fight off Sliske's first wave of wights. The brothers refuse to help Sliske and vow to kill him for all the agony he caused. Sliske sends his standard wights at the brothers in the Shadow Realm while he sends Nomad, Linza and Gregorovic at the player.
The brothers work together to defeat the wights and return to their mounds. Linza reveals that they are doing well and are happy to be free of Sliske's hold over them.