The Primarchs were the twenty genetically-engineered "sons" of the Emperor. The Emperor used his own DNA in their creation, and they were designed to be far superior to the average human: immensely larger, stronger, hardier, faster, and more intelligent. They were also incredibly charismatic, as their main role was to be generals and leaders of the Imperial military. They were created in a secret underground laboratory on Luna under tightest security. However, the forces of Chaos somehow managed to spirit them away just prior to their maturation and it is speculated that they also managed to tamper with the infant Primarchs. These were scattered across the galaxy, beyond the Emperor's reach, and all of them landed on different worlds. The Emperor could sense that the infant Primarchs were alive, but was unable to reach them. Therefore he used their previously collected DNA samples to create the Space Marines. The genetic material of each one of them was used to found a single Space Marine Legion, twenty in total. Their homeworlds and their infancy would influence and mould them to a large extent. There they quickly grew to adulthood and often rose to power, ruling, leading, and helping the inhabitants. As the Emperor found them, he was generally pleased by their actions, and quickly gave them the leadership of their respective legion. The first Primarch to be found was Horus, who became the Emperor's favourite. Most Primarchs somehow recognized the Emperor on sight, and immediately pledged their allegiance on the spot. A few, (Leman Russ, Ferrus Manus and Vulkan) only followed Him after being bested in contests. Angron refused, and was abducted from his homeworld, something he never really accepted. The last to be found was Alpharius. At the end of the Great Crusade Warmaster Horus fell to Chaos, and eight of his fellow Primarchs followed him against the Emperor, resulting in a full-scale civil war known as the Horus Heresy. Each Primarch chose his side, loyalists against traitors, leading their legions against their former comrades.