One of the foundation elements of Warhammer 40k lore is the idea that the Emperor created 20 Primarchs, who were snatched from Terra by a Chaos vortex and scattered around the galaxy.
This was published at least as early as 2002 in the Index Astartes.
Eventually, all 20 would be recovered, lead their own Space Marine legion and all would participate in the Great Crusade.
For the order of recovery, the Lexicanum is a good resource. Their order:
- I Lion El'Jonson The Lion 11
- III Fulgrim The Phoenician 5
- IV Perturabo The Lord of Iron 12
- V Jaghatai Khan The Great Khan, The Warhawk 15
- VI Leman Russ The Wolf King, The Great Wolf 2
- VII Rogal Dorn The Emperor's Champion, The Praetorian of Terra 7
- VIII Konrad Curze The Night Haunter, The Lord of the Night 16
- IX Sanguinius The Great Angel 10
- X Ferrus Manus The Gorgon 4
- XII Angron The Red Angel, The Lord of the Red Sands 17
- XIII Roboute Guilliman The Battle King, The Avenging Son 8
- XIV Mortarion The Death Lord, the Reaper of Men 13
- XV Magnus the Red The Crimson King, The Red Cyclops 9
- XVI Horus Lupercal The Warmaster, 1
- XVII Lorgar Aurelian The Urizen, The Golden One 14
- XVIII Vulkan The Lord of Drakes 6
- XIX Corvus Corax The Raven-Lord 18
- XX Alpharius Omegon The Last Primarch, The Lord of Serpents 20
- ** Note that while II and XI exist, records of II and XI were expunged from Imperial records.
The only other problem then is that Omegon appears to be a hook thrown in.
As I understand, the primarchs were snatched while still in their “incubation capsules” — their bio-engineering growth crèche; then Alpharius split into an identical twin while still gestating within his capsule.
Being as least coy as possible with numbers of souls versus numbers of bodies or cylinders, what is the canon answer to the number of primarchs? Is this whole deception of the reality of 21 canon, does canon count it as no deception because the twins exist as a single soul as if Omegon is some sort of slave-botted hack, or is Omegon technically even a Primarch?