First Founding

The First Founding of the Space Marine Legions, also originally called the Legiones Astartes, occurred in the late 30th Millennium after the end of the Age of Strife and the Unification Wars that founded the Imperium of Man on Terra. Eighteen known Space Marine Legions were created from the gene-seed of the 18 known Primarchs engineered by the Emperor of Mankind from his own genetic code in his laboratory in the Imperial Palace on Terra beneath the Himalayan Mountains. In spite of the fact that the Primarchs were separated from the Emperor of Mankind through the mysterious actions of the Ruinous Powers of Chaos and scattered through the Warp across the galaxy, he managed to keep a small sample of each Primarch's gene-seed, and use this genetic material to create the first Space Marines by further genetically enhancing his own elite, Terran-born soldiers. With each Primarch the Emperor re-discovered during the Great Crusade, he gave command of the Space Marine Legion created from their genetic material back to them. Each Primarch then set up their Legion's headquarters on his homeworld, from which they also recruited new Space Marines into the Legion. Two other Legions, the II Legion and the XI Legion and their Primarchs, were created by the Emperor, but nothing is known of what became of these Legions and their Primarchs and all data pertaining to them has been deleted from current Imperial records.

First Founding Space Marine Legions

Legion Number	Primarch	Legion	Loyalty	Primarch Status
I	Lion El'Jonson	Dark Angels	Loyal (Ambiguous)	Mortally Wounded by Luther, leader of the Fallen Angels
II	Missing and deleted from Imperial records
III	Fulgrim	Emperor's Children	Traitor	Despite being possessed by a Greater Daemon of Slaanesh who impersonated him for a time, Fulgrim regained control of his body and eventually became a Daemon Prince of Slaanesh
IV	Perturabo	Iron Warriors	Traitor	Alive; Daemon Prince of Chaos Undivided
V	Jaghatai Khan	White Scars	Loyal	Missing
VI	Leman Russ	Space Wolves	Loyal	Missing
VII	Rogal Dorn	Imperial Fists	Loyal	Dead (Ambiguous)
VIII	Konrad Curze (Night Haunter)	Night Lords	Traitor	Dead
IX	Sanguinius	Blood Angels	Loyal	Dead
X	Ferrus Manus	Iron Hands	Loyal	Dead
XI	Missing and deleted from Imperial records
XII	Angron	World Eaters (War Hounds)	Traitor	Alive; Daemon Prince of Khorne; Banished to the Warp following the First War for Armageddon
XIII	Roboute Guilliman	Ultramarines	Loyal	Mortally Wounded; Now in stasis
XIV	Mortarion	Death Guard (Dusk Raiders)	Traitor	Alive; Daemon Prince of Nurgle
XV	Magnus the Red	Thousand Sons	Traitor	Alive; Daemon Prince of Tzeentch
XVI	Horus	Luna Wolves	Traitor	Dead
XVII	Lorgar	Word Bearers (Imperial Heralds)	Traitor	Alive; Daemon Prince of Chaos Undivided
XVIII	Vulkan	Salamanders	Loyal	Missing
XIX	Corax	Raven Guard	Loyal	Missing
XX	Alpharius Omegon	Alpha Legion	Traitor, possibly still Loyal	One twin dead, slain by Roboute Guilliman; other's fate unknown

Sources

• Warhammer 40,000 Rulebook (5th Edition)
• Codex: Space Marines (5th Edition)
• Codex: Chaos Space Marines (4th Edition)