The Skull Helm is the Power Armour helmet worn by a Space Marine Chaplain that is often carved to resemble the face of a human skull, an ancient symbol of death now used to mark the memory of the Emperor of Mankind's great sacrifice for humanity during the Horus Heresy.
The armour of a Space Marine Chaplain is a daunting sight, adorned with icons of battle and death. Every aspect of a Chaplain's garb serves as a reminder of mortality's impermanent nature, and thus, the significance of preserving the immortal soul. One of the most iconic elements of a Chaplain's wargear is his Skull Helm, a stern visage that evokes the Emperor's wrath and terrible sacrifice. These helms may take many different forms and have been crafted by numerous Space Marine artificers across the galaxy. Universally, however, they are all fearsome in aspect.
- Deathwatch: Rites of Battle (RPG), pg. 143