It was Rembrandt who christened the group of Guardians the "Brotherhood", of which he was an active member. He was also the last Guardian to join the Brotherhood during its time of openness amongst its members about its existence. After his first son Aaron died sacrificing his life to stop a nuclear attack launched by the Dark Legion's GrandmasterMenniker and a band of Overlanders, Rembrandt was consumed by grief, even more so than the other Guardians. When his younger son, Jordan, then requested to be trained as a Guardian, he agreed, but set up a new code of restrictions and guidelines involving the raising of the Guardians and their knowledge of the Brotherhood, putting a greater emphasis on self-reliance at a young age to prevent further Guardians from perishing as Aaron had. Despite Harlan and Moonwatcher's objections to this new method of training, it was adopted by the Brotherhood and was carried down through the generations through to the time of Knuckles. (KtE: #25)
A brown Echidna, Rembrandt wore a yellow vest, glasses, green gloves and boots and had white bands on his dreadlocks. Unlike most other male echidnas, Rembrandt had tan hair on his head distinct from his fur and, like other members of the Brotherhood, sported a beard. In the afterlife, Rembrandt was seen wearing spiked guardian gloves.