Rubric Marines
"Immortality is a terrible curse."
-Simone de Beauvoir
Rubric Marines - the cursed automatons of the Thousand Sons, and one of the two toughest infantry units that are available to the Traitor Legions, right alongside their Nurglite rivals, the Plague Marines. They serve a similar tactical role in that they're absolutely tough as balls, but whereas the Plague Marines, owing to their diseased bulk, can resist large volumes of anti-infantry fire, the Rubric Marines, protected by dark sorcery, will shrug off even the most powerful hits from anti-tank weapons.
They've been known to get pre-5th Edition Necron players to rage-quit.