The Brotherhood of Guardians began with Steppenwolf inheriting the title of Guardian from his deceased father, Edmund, and battling the Dark Legion. As the years passed, Steppenwolf's descendants joined him in watching over Angel Island, and it was his great-grandson Remembrandt who first suggested the name Brotherhood. Early on, the group's operating methods and existence were known to all its members, even the current Guardian, until the first death of one of their number since Edmund: that of Aaron. Afterwards, the Brotherhood created a code of conduct that involved hiding from the people of Mobius, their existence hidden from all but a handful of allies, and of course their ancestral enemies, the Dark Legion, and observing Mobius as a whole while the youngest member defended Angel Island itself against such threats as the Dingoes and the Overlanders. With only a few exceptions, the Brotherhood had no contact with anyone from the outside world. This continued for 400 years, right up until Knuckles became the active Guardian of Angel Island.
The House of Acorn formed a friendship of sorts with the Brotherhood during the years between the Great War with the Overlanders and the later war with Dr. Robotnik. Because of political differences, however, the two groups never truly aligned with each other, not even against the threat posed by the second Dr. Robotnik. When Princess Sally Acorn met with the Brotherhood to discuss their providing support to the beleaugered people of Knothole, the Guardians refused to grant her request. The main reason for this was that the Brotherhood's main offering would include munitions technology, something that the Kingdom of Acorn's traditional laws forbade the use of and that Sally personally loathed.
Despite their usual missions of observing Mobius, the Brotherhood members have gotten involved in matters personally. Such occurrences include when the disguised Guardians threw Monk, Knuckles' childhood tormentor, off the edge of Angel Island. They later atoned for this in a way by holding Hunter, the human responsible for Monk's death, in prison. Later, members of the Brotherhood led by Guardian Mathias attacked the Dark Legion stronghold at the Grand Conservatory, resulting in Mathias' death. The living members of the Brotherhood, with the exception of Knuckles, were then transported to the Twilight Zone, only to be brought back by Knuckles' himself. During Knuckles' brief death, all the deceased members of the Brotherhood, from Steppenwolf down to Tobor and including Janelle-Li, appeared with him at his own funeral to begin explaining his evolution to a higher plane of existence to him.
During Sonic's exodus in space, a result of the battle with the Xorda, all living members of the Brotherhood except for Locke and Knuckles, with the exception of Athair, as he is not technically a member of the Brotherhood any longer, disappeared mysteriously. This apparently occurred when they worked together to hold off Dr. Robotnik's attempt to seize the Master Emerald. Later on, Dr. Finitevus supplies Locke with the apparent location of his missing family, tricking Locke into passing on the Guardian duties to him and sending him off with a Warp Ring to undertake his search. The white furred Echidna later revealed to Scourge the Hedgehog that he had captured the Brotherhood after their battle with Robotnik's forces, experimenting on them to learn what he could about their use of Chaos energy before banishing them to the Twilight Zone.
Knuckles the Echidna