The Ultramarines are, in many ways, the exemplars of the many Chapters of the Space Marines. Their mighty Primarch, Roboute Guilliman, wrote the Codex Astartes, a tome which lays the foundation of tactics, heraldry, and combat doctrine by which most Adeptus Astartes operate. In battle, they use every resource available to them, deploying specialised units to execute their missions with discipline and efficiency.