In the wake of the Battle for Macragge, Caito Galenus became the Captain of the Ultramarines 5th Company, the last of the four Battle Companies. He is also Master of the Marches. Captain Galenus's predecessor as 5th Company Captain was Cato Sicarius, the current 2nd Company Captain.
As the Master of the Marches, it is Galenus' task to guard the approaches to Ultramar and attend to threats building beyond the empire's borders. To this end, Galenus has built strong ties with the Chapter's Shipmasters. His company makes substantial use of orbital supporting assets, each strike force typically being assigned to a specific Sword-class frigate or Strike Cruiser for the duration of each tour outside of Ultramar. Galenus himself is a master of space warfare and has commanded numerous warships in his time. He is known for his expertise in zero-gravity combat, ship-to-ship boarding actions and planetary drop assault. Where possible he prefers to observe his enemies from afar, making substantial use of Vanguard forces to scout out the foe.
Sometime in M42 he led an Ultramarines strike force to aid Vackenides, after it was invaded by the forces of Chaos. The world was later declared lost, however, and Galenus' strike force fought to buy time for hundreds of thousands of its citizens to be evacuated from the space port Helice. The Ultramarines then fought a horde of Heretics, that were aided by Chaos Space Marines and a Chaos Titan. Galenus' forces suffered numerous losses at the Titan's hands and even the relic Land Raider Fist of Guilliman was left heavily damaged. After Chaplain Tavian told the Captain that the Land Raider could not fall into the Heretics' grasp, Galenus ordered Tavian to take a small force to save the Fist. Afterwards, the Captain knew the Titan would slay them all, if it was not destroyed. In desperation he led his forces in a charge against it, hoping to get inside the Titan's shields so they could damage it. Though it raked them with fire, Galenus and his surviving forces succeeded and were able to destroy the Titan's plasma generators with their combined firepower. The Titan then exploded and while more of his Ultramarines were killed by the Titan's death, Galenus survived. He then continued to lead his remaining Ultramarines against the surviving forces of Chaos.
- 1: Codex: Space Marines (5th Edition), pg. 17
- 2: Codex: Space Marines (3rd Edition), pg. 46
- 3: Dark Imperium (Novel), Chapter 10
- 4: Codex Supplement: Ultramarines (8th Edition) pg.16
- 5: Codex: Space Marines (9th Edition), pgs. 74-77