The icon of the Adeptus Custodes
An Armour Thrall is the name given to the normal humans who have been bonded as life-long servants of the Adeptus Custodes and assist them in battle. Armour Thralls are well-trained and skilled combatants in their own right. Their primary duty is to carry extra ammunition and armour sealant for their assigned Custodian when in combat.
When the Bolt Caster built into the Custodian's primary weapon -- usually a Guardian Spear or Sentinel Blade -- are empty, the Custodian tosses the weapon to the Armoury Thrall. The Thrall reloads it and is strong enough to throw the weapon back to the Custodian.
Sources[]
- Master of Mankind (Novel) by Aaron Dembski-Bowden, Ch. 23