Primarchs

The Primarchs were the 20 genetically-engineered transhuman sons of the Emperor of Mankind created in the late 30th Millennium after the end of the Unification Wars. They were intended to be the immortal and superhuman leaders who would command the Emperor's Great Crusade to reunite the scattered human race beneath His leadership. Their genomes later served as the genetic templates from which the Emperor crafted His 20 Space Marine Legions. They were bred to be perfect generals, warriors and statesmen; larger, stronger, faster, and smarter than any normal human could ever hope to be.

They possessed a charisma and martial prowess that made them like the mythical gods of old, untouchable by disease, old age or supposedly the petty failings of lesser men. The Primarchs were the Emperor's answer to reclaiming all the lost worlds of Mankind, and welcoming them into His new Imperium. The Emperor intended to raise His sons to be the best military commanders and political leaders Mankind had ever known, and they would bring the Imperial Truth to the rest of the human-settled galaxy in their father's name. Yet for all their gifts, the Primarchs were still men, and in the end their very human flaws would become the primary obstacle to the realisation of the Emperor's great dream for Mankind.

Order of Rediscovery of the Primarchs
The following is a definitive list of the order in which the Primarchs were rediscovered by the Emperor of Mankind during the Great Crusade starting in 797.M30: Note: Much of the text here has been copied from the affiliate Warhammer 40,000 Wiki under the Fair Use doctrine.