Roughly 28,000 years in the future, the Emperor of Mankind creates twenty genetically engineered superhumans called "Primarchs." Demigod-like giants, their genomes were based on the Emperor's own genome; making them, in a way, his sons. The Emperor then creates the Space Marines for his armies. Just as the Primarchs are the genetic sons of the Emperor, the Space Marines are the genetic sons of their Primarch. There were twenty Space Marine Legions, one for each Primarch, who became the commander of his respective Legion.