2. Cybots, super-warriors in a metal coffin
Even the seemingly invincible Space Marines are not immortal with their long lives, although none of them ever dies of natural causes. Usually, the Codex Astartes stipulates recovering the gene-seed of a fallen brother to create new Space Marines.
However, an exception is made for the greatest of their heroes who have rendered particularly great services to the Imperium. If a Space Marine lies dying and cannot be saved, there are two paths available to him: The Emperor’s grace (i.e., the honorable death) or embedding in a Cybot or Dreadnought.
Cybots are huge walkers, coffins made of metal, into which dying Space Marines are embedded to continue fighting as living war machines. They serve the Imperium even in death and beyond.
A Dreadnought is equipped with so many weapons and such strong armor that just one can outweigh several Space Marines. However, these particularly honored brothers are only called upon in emergencies because their existence as living machines drives them slowly insane. So while Cybots can become ancient, they are only awake for a fraction of that time.
