The Flaxans

The Flaxans are an alien race in the Invincible comics who come from another dimension, one in which time passes much faster than on Earth. They attack Earth more than once; after a later invasion, Robot and Monster Girl follow them back through a portal to finish them for good and end up trapped there for nearly a thousand years of subjective time, returning only a year after they left (Amanda's body has aged twelve years). It is later revealed that the two overthrew the Flaxan dictatorship and ruled the dimension themselves, until political strife split them and Robot became more ruthless in trying to improve his subjects' lives.