The Aegis Cluster is a region within Microspace. Known planets within it include Aegis-3 and the desert world Aegis-6. It was previously home to the Sandmen mercenary caste.
Baron Karza was born on Aegis-6, and was raised by the Sandmen, rising quickly through their ranks. Baron Karza's profile The warrior who would become known as Acroyear hailed from Aegis-3, and was a "rising star" amongst the Sandmen. Acroyear's profile
At some point after becoming close to the Emperor, Karza had the Sandmen forcibly conscripted and converted into Acroyear warriors. Baron Karza's profile
While fighting a partially sentient Dire Wraith virus, Acroyear swore by the "suns of Aegis". ROM: First Strike