Rubric Marines
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, the Rubric Marines, protected by dark sorcery, will similarly shrug off heavy weaponry.
They've been known to get previous-edition Necron players to rage-quit.
Lore
The Rubric Marines were once basic Chaos Marines in the Thousand Sons. Due to the rampant use of Sorcery by the Sons, the legion as a whole began to suffer horrifying, increasingly-debilitating mutations. This generally sucked, since it meant that increasingly, members of the legion were turning into that which must never be named. Tzeentch, in the Chaos God's proud tradition of not giving a fuck, left the Sons to work out their own solution to the problem, likely so he'd have some entertainment over the weekend.
At some point, trying to help fix this little mutation epidemic, a Sorcerer called Ahzek Ahriman broke into the personal library of Thousand Sons Primarch Magnus the Red, and bogarted the choicest and most powerful of his spellbooks. Using them, he crafted a way to undo the mutations plaguing the legion, and cast an incredibly powerful spell called the Rubric of Ahriman. The spell was successful in stopping the mutation, but only really amongst the command staff - every non-Sorcerer in the legion was reduced to dust and trapped as bound spirits within their sealed power armor for eternity (or at least until the armor was destroyed). Suffice to say, Magnus was really pissed off and wanted to blow Ahriman up with mind-bullets, but Tzeentch asked him not to because that was some pretty epic douchebaggery. So Magnus kicked him out of the Thousand Sons, instead.
What a dick.
Since the Rubric of Ahriman, the Thousand sons have lost many of their Rubric Marines, but the rite has snuck out of the hands of the Legion that began it, and now several legions can produce more Rubric Marines by continuing the rite on a smaller scale. It's ironic, as the fluff states, they were turned from a legion of scholars and book lovers, into mindless, walking power armors that can't even think!. They can think, its just that they've lost all hope and purpose in life. Reduced from scholars to beings who can't even feel, they let the days slip into millennia. Only battle barely reminds them of what it was to be alive, and they fight accordingly. So grimdark.
They're also central to this tomfoolery, so props for that.
On The Tabletop
Rubric Marines are absolutely terrifying on the tabletop. They aren't quite as good as ignoring the sustained fire of 40 Shoota Boyz as their counterparts, the Plague Marines are, but unlike them they can ignore a direct Battle Cannon shot, since Rubrics possess a phenomenally-dickish 4++ invulnerable save, and, just like their counterparts, can score. Even better, Rubric Marines pack Inferno Bolts, which means their Bolters are AP3. Suffice to say, they can carve through a squad of MEQ effortlessly, and, prior to their massive Tomb Kings in Space update, fielding one squad of intelligently-managed Rubric Marines essentially guaranteed victory against a typical Necron player. They're also led by a Sorcerer, who gives them access to one psy power (typically something like Bolt of Change, so the squad can pop transports). The Sorcerer's Bolt Pistol also has Inferno Bolts.
Rubrics are cursed with Slow and Purposeful, and unlike the other aligned Chaos Marines, do not have close combat weapons or bolt pistols. At a glance, this makes them a very easy-to-target melee weak-spot, but in practice, this isn't quite true; they still have their beefy-as-shit 3+/4++ saves, even though they hit at initiative 1, and the Sorcerer's Force Weapon means that no MC worth their shit will get anywhere near them. What they are vulnerable to is being Tarpitted, due to their relatively lackluster number of attacks and immense focus on shooting to take advantage of their juicy AP 3 Bolter shots.
Rubrics benefit heavily from having a Rhino Transport. Not because they need the survivability (they're tougher than the vehicle they're in, to be frank), but because the mobility they get is such an enormous boon. Take full advantage of their ability to shoot out of their transport, and use it in glorified Tzeentchian drive-by shooting, before disembarking in rapid fire range and warpfire-blasting a bitch.
They are, however, retardedly expensive, and even more so with an Icon of Fire.