Rembrandt was a Mobian Echidna, son of Harlan and the father of Aaron and Jordan; the only pair of siblings ever born in the line of Guardians. He was responsible for naming the Guardians who had ended their duty the Brotherhood of Guardians and started the tradition of raising the next generation of Guardian without them knowing of this organization. Hundreds of years after his death, his spirit attended the funeral of his descendant Knuckles and witnessed him being taken to Aurora's Virtual Zone.
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 among 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 Grandmaster Menniker 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.
Hundreds of years later, Rembrandt met his descendant Knuckles, along with the other deceased Brotherhood members, during Knuckles' brief time in the afterlife.
- His name is likely a reference to the Dutch artist Rembrandt Harmenszoon van Rijn.