The Diasporex was a nomadic civilisation of humans and aliens who lived aboard a vast collection of starships, maintaining a network of hydrogen collector space stations around various stars to fuel their vessels' power generators. They had been prowling the depths of space since the Age of Strife and their lifestyle may have evolved as a reaction to the horrors of that time on many human-settled worlds. During the last days of the Great Crusade in the early 31st Millennium, the Iron Hands Legion encountered the fleets of the Diasporex.
The Iron Hands offered the human members of the Diasporex the opportunity to separate from their alien allies and to join the Imperium of Man. They declined, and so under standing Imperial orders had to be destroyed as a potential threat to the nascent Imperium. In the months that followed, the Iron Hands Legion fleet tried to destroy the Diasporex, but their fleets proved to be highly skilled and experienced in naval warfare: they easily evaded multiple fleet engagements initiated by the Astartes and even managed to damage an Iron Hands Cruiser.
At this point, the Emperor's Children Legion were called in as reinforcements for the Iron Hands. The combined Astartes force eventually made the discovery that the Diasporex used hidden space stations to collect hydrogen fuel from various local stars, which was the reason why they had remained in that sector of space rather than just fleeing from the Imperial forces. The Space Marines assaulted these stations and thus forced the Diasporex fleet into open battle to protect them, where they were defeated.
A brief shipboarding action occurred, in which the Emperor's Children Captain Solomon Demeter stole the glory of seizing the Diasporex flagship from the increasingly corrupted Primarch Fulgrim. The final words of the alien Diasporex flagship captain were, "We only wished to be left alone."
- Fulgrim (Novel) by Graham McNeill