The Bucephelus maintained a garrison of the Legio Custodes and took part in the titanic Battle of Gyros-Thravian when the Emperor was forced to deploy the Custodians to reinforce the Space Marines of the Imperial Fists, Luna Wolves and Death Guard Legions in their fight against the Orks of Warboss Gharkul Blackfang.
At some time during the Great Crusade, the Emperor moved His flag to the Imperator Somnium.
Bucephalus was the name given to the beloved warhorse of Alexander the Great.
- The Horus Heresy: Collected Visions (Art Book), "The Custodian Guard," pg. 143
- The Wolf of Ash and Fire (Short Story) by Graham McNeill