Horus Heresy

The Horus Heresy was a period in which a bunch of loyal subordinate good-guy Marines followed their good-guy Warmaster against the tyranny of a guy that called himself “Emperor of mankind”.  This “Emperor”, currently: a rotting statue, is still to this day being held accountable for his crimes against humanity and other alien races. Contrary to popular belief, there were no outside influences involved in the Horus Heresy. As much as they would have you think otherwise.