The "now You're A Problem" Assaward

This ass spent years being underestimated, overlooked, and quietly filed under harmless, and they took careful notes the entire time. Nobody saw them coming, which was, in retrospect, the whole plan. Then one day the ignored becomes the undeniable, the background character steps into the light, and a great many people who did not take them seriously are suddenly, urgently taking them seriously. The radar they flew under is now blaring. They did not get loud. They got good, patiently, in the dark. A sleeper who woke up exactly on schedule, and everyone who slept on them is now wide awake and mildly panicking. Stay underestimated, you patient, inevitable legend.