In the fictional universe of Warhammer 40,000, the Primarchs were the twenty cloned sons of the Emperor, born leaders of his Space Marine legions. They were bred to be nearly perfect: larger, stronger, faster, and smarter than normal humans. Their genetic material was also used to form the basis of the legions they would command.

However, the forces of Chaos somehow spirited the children away, scattering them across the galaxy. All but two were discovered on remote worlds, where they had quickly grown to adulthood, and often held leadership of their adoptive worlds. When the Emperor found them, he gave them leadership of the Space Marine legions created from their genetic material.

Following the Great Crusade, Warmaster Horus fell to Chaos, and he convinced eight of his fellow Primarchs to rebel against the Emperor and follow him. In the Horus Heresy, brother fought brother as the Primarchs led their legions against their former comrades; Horus himself fought Sanguinius and the Emperor, killing Sanguinius, but dying at the hand of the Emperor. The Traitor Legions fled to the Eye of Terror.

Primarchs & Respective Legions

1. Lion El'Jonson - Dark Angels - Loyal
2. missing
3. Fulgrim - Emperor's Children - Traitor
4. Perturabo - Iron Warriors - Traitor
5. Jaghatai Khan - White Scars - Loyal
6. Leman Russ - Space Wolves - Loyal
7. Rogal Dorn - Imperial Fists - Loyal
8. Night Haunter - Night Lords - Traitor
9. Sanguinius - Blood Angels - Loyal
10. Ferrus Manus - Iron Hands - Loyal
11. missing
12. Angron - World Eaters - Traitor
13. Roboute Guilliman - Ultramarines - Loyal
14. Mortarion - Death Guard - Traitor
15. Magnus the Red - Thousand Sons - Traitor
16. Horus - Luna Wolves - Traitor
17. Lorgar - Word Bearers - Traitor
18. Vulkan - Salamanders - Loyal
19. Corax - Raven Guard - Loyal
20. Alpharius - Alpha Legion - Traitor

Fan speculation places Sigmar as one of the two missing Primarchs.