The Mortal Majority is the broad resentment bloc produced by a civilization in which elites can buy longevity, backup, enhancement, and narrative protection while most people remain exposed to ordinary risk. It is less an organization than a recurring political force.
Different factions recruit it with different promises. Some offer egalitarian redistribution. Others offer scapegoats. The movement matters because every posthuman order in Sol has to decide whether to appease the mortal many or merely manage them.