In his labs on Terra, the Emperor created twenty Primarchs. The secrets behind their creation are closely guarded, and none know how the Emperor managed to create such beings. They were to be the epitome of men; their martial skill and power only matched by the sheer force of their charisma and personality. They were to be gods among men.
Tragically, an accident within the Emperor's labs scattered the Primarchs across the galaxy before they were fully grown. Thankfully, however, the Emperor still had the gene templates with which the Primarchs were created, and he used these to create the Space Marine Legions. It was with these Legions that he began the Great Crusade, to reuinte all of humanity into one glorious Imperium.
Over the course of the Great Crusade, the Emperor discovered his missing Sons one by one, and he gifted each of them with command of the Space Marine Legion which had used their genetic template. Sadly 2 Primarchs remained missing.
 The Horus Heresy
Two hundred years after the start of the Great Crusade, Horus, the greatest and most favoured of the Primarchs, turned to the Runious Powers of Chaos and betrayed his father, the Emperor. Horus' power and influence enabled him to bring fully half of the Emperor's legions to his cause, causing the galaxy to erupt in the most horrific civil war imaginable. The death toll mounted into trillions on each side as Horus fought to claim what he percieved was his rightful place as ruler of Humanity, rather than the Emperor.
The war, dubbed the Horus Heresy, culimated in a titanic duel between Horus and the God-Emperor himself. The Emperor was mortally wounded, but Horus was utterly obliterated. The legions under Horus' command fled to the Eye of Terror, a warp-realspace overlap, and have become Chaos Space Marines.
 List of Primarchs
These are the Primarchs that stayed true to the Emperor and fought for him.
- Lion El'Johnson of the Dark Angels - Johnson was lost soon after the Horus Heresy ended, after a masive battle on the Dark Angels home planet of Caliban. The details of the conflict are known to none outside the Dark Angels Chapter themselves.
- Vulkan of the Salamanders - Close quarter fighting specialists. The Salamanders Legion was decimated during the Drop Site Massacre, forcing them to withdraw from the majority of the fighting. Even now, the Salamanders remain significantly under strength comapred to most modern-day Chapters of Space Marines. Vulkan himself disappeared seventy years after the end of the Heresy.
- Roboute Gulliman of the Ultramarines - Gulliman was the Primarch who held the Imperium together in the horrific days immediately following the Heresy, utilising the abilities of his massive Legion to maximum effect. He was defeated by the Fallen Primarch Fulgrim several years after the end of the Heresy, though some say he is still alive.
- Leman Russ of the Space Wolves - disappeared after the end of the Heresy, claiming he will return for the "Wolftime."
- Corax of the Raven Guard - Stealth and sabotage specialist. Disappeared after the Horus Heresy with a single word of valediction - "Nevermore."
- Sanguinius of the Blood Angels - most beloved of all the Primarchs, Sanguinius was killed by Horus in the closing moments of the Heresy. But it took the death of the Angel to finally show the Emperor that Horus was beyond help, enabling the Emperor to find the resolve in him to kill Horus.
- Jaghati Khan of the White Scars - Mobile and rapid attack specialist. After the Heresy, he followed a band of Dark Eldar back to their shadow city. He has not been seen since.
- Ferrus Manus of the Iron Hands - killed by Fulgrim in the opening stages of the Heresy, during the Drop Site Massacre.
- Rogal Dorn of the Imperial Fists - Siege specialist. Along with the Blood Angels and White Scars, the Fists had the honour of defending the Imperial Palace against Horus. After the Heresy, Dorn assaulted a Chaos Frigate single-handedly, which then performed an emergency warp jump with him still aboard. He has not been seen since.
These are the Primarchs who betrayed the Emperor.
- Horus of the Luna Wolves - the Luna Wolves were later renamed to Sons of Horus in honour of their leader, and then finally Black Legion to expunge Horus' name because of his failure to conquer the galaxy.
- Mortarion of the Death Guard - ascended to Daemonhood and now resides in the Eye of Terror.
- Fulgrim of the Emperor's Children - ascended to Daemonhood and now resides in the Eye of Terror.
- Magnus of the Thousand Sons - ascended to Daemonhood and now resides in the Eye of Terror.
- Angron of the World Eaters - Assault specialist. Defeated by one hundred Grey Knight Terminators during the First War of Armageddon, and was banished back to the warp.
- Alpharius of the Alpha Legion - Stealth and sabotage specialist. Supposedly killed by Gulliman soon after the Heresy, but this is subject to debate.
- Konrade "Night Haunter" Curze of the Night Lords - killed by a Callidus Assassin, M'Shen, after the Horus Heresy.
- Perturabo of the Iron Warriors - Siege specialist. Ascended to Daemonhood and now resides in the Eye of Terror.
- Lorgar of the Word Bearers - Ascended to Daemonhood and now resides in the Eye of Terror.
 Position of a Primarch
The position of Primarch is the founding leader of a Space Marine chapter. The Primarch is the figurehead to whom worship, after the Emperor, is directed. Not all Primarchs live in the present time of the 40,000K universe but they are still considered by their chapters to be living gods. This means that the chapters base their principles and teaching around what the Primarch himself stood for.
Second only to the Emperor in power, the Primarchs wield great authority in the 40K universe.