First Founding

After he conquered Terra, the Emperor of Mankind set out on a Great Crusade to re-unite the lost human colonies into a mighty Imperium. He soon realized that bog-standard humans wouldn't be enough; some situations called for a small number of devastatingly powerful warriors, a surgical strike force to smash enemy linchpins. To fill this role, he created his Primarchs, and from their genes, he created the Legiones Astartes, the twenty Space Marine Legions:

Legion Number	Primarch	Homeworld	Name of the Legion	Allegiance	Tarot Character*
I	Lion El'Jonson	Caliban	Dark Angels	Loyal	THE HERMIT
II	+++Records expunged+++
III	Fulgrim	Chemos	Emperor's Children	Traitor	THE EMPRESS
IV	Perturabo	Olympia	Iron Warriors	Traitor	THE DEVIL
V	Jaghatai Khan	Mundus Planus	White Scars	Loyal	TEMPERANCE
VI	Leman Russ	Fenris	Space Wolves	Loyal	THE LAST JUDGEMENT
VII	Rogal Dorn	Terra	Imperial Fists	Loyal	THE SUN
VIII	Konrad Curze	Nostramo	Night Lords	Traitor	THE MOON
IX	Sanguinius	Baal	Blood Angels	Loyal	THE HANGED MAN
X	Ferrus Manus	Medusa	Iron Hands	Loyal	JUSTICE
XI	+++Records expunged+++
XII	Angron	Unknown	World Eaters	Traitor	THE TOWER
XIII	Roboute Guilliman	Macragge	Ultramarines	Loyal	THE CHARIOT
XIV	Mortarion	Barbarus	Death Guard	Traitor	DEATH
XV	Magnus the Red	Prospero	Thousand Sons	Traitor	THE MAGUS
XVI	Horus	Cthonia	Luna Wolves/Sons of Horus	Traitor	THE EMPEROR
XVII	Lorgar	Colchis	Word Bearers	Traitor	THE HIEROPHANT
XVIII	Vulkan	Nocturne	Salamanders	Loyal	STRENGTH
XIX	Corax	Deliverance	Raven Guard	Loyal	THE STAR
XX	Alpharius Omegon	Unknown	Alpha Legion	It's very complicated	THE LOVERS

• Tarot Details come from http://menducia.atspace.com/primarchs/IV.html

The two Lost LEGIONS align with the Second card II - The High Priestess and the Tenth Card X - Fortune. From a pure Conjecture standpoint the Characters of the Tarot align well with the 20 Primarchs and this gives a good base to suppose the attributes of the two missing primarchs.

Horus Heresy

For all their power, the Space Marines and Primarchs were not perfect; half of them were sufficiently flawed to be tempted by (or driven to) Chaos, led by Warmaster Horus. The traitors were defeated, but at a terrible cost, including the near-death of the God-Emperor of Mankind and trillions of deaths.

Roboute Guilliman decided that the so-called Horus Heresy was proof that one man could not be trusted with power over one-twentieth of the Imperial Armed Forces, so he enacted several reforms to divide the Imperial Army into the Imperial Guard and Navy, and split the remaining loyalist Legions into Chapters, in accordance with his Codex Astartes. This event was later known as the Second Founding.

<nowiki>Insert non-formatted text here</nowiki>==Two Unknown Legions==

In the First Edition of Warhammer 40,000, the twenty First Founding Chapters were all known. It seems that Games Workshop had more love for some than others; when they made fluff revisions in the transition to Second Edition, the Valedictors and Rainbow Warriors were demoted to one of the "Later Foundings."

Nowadays, nothing concrete is known about the Legions II and XI, and likewise their unknown Primarchs. It is suggested that the Space Wolves destroyed them for some reason, and in the Horus Heresy book The First Heretic, a daemon suggests to the Word Bearers that the eleventh Legion in particular did something really bad, and that the left-over Marines were folded into the Ultramarines.