The Imperium of Man is the apex of human society, spanning the majority of the galaxy and consisting of many hundreds of trillions of Humans. Under the ever-seeing eye of the Emperor, it's military might is unmatchable and it's Imperial Guard and Space Marines are the finest fighting forces ever to be assembled. Xenos scum and heretical traitors fall by the thousands before it's mighty guns, it's terrifyingly powerful planet-killing fleets of starships, it's armoured tanks and troopers.
For the Imperium of Man! Charge you dogs!