Dark Guardian

To the Autobots, the Guardian robots are a reassuring sight, knowledge that they are safe. It was not always so. For the Guardian robots have a horrifying ancestor, the Dark Guardians, who enforced the reign of the Quintessons during their god-forsaken rule of Cybertron.



MUX Canon
Since the third-season Aerialbot-time-travel episode has yet to happen, only Alpha Trion and a few others recall the horror of the Dark Guardians.