Necron

Space zombie terminator egyptians. That was Space Zombie Terminator Egyptians. Yeah.

"Death is frightening, and so is eternal life."
-Mason Cooley

“That is not dead which can eternal lie,
And with strange aeons even death may die”
- H.P. Lovecraft

'My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!'
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare
The lone and level sands stretch far away.

-Percy Bysshe Shelley, "Ozymandias"

Finally.
After our Thousand Year Old Slumber, WE ARE FINALLY ALIVE.
For eons I have awaited this day.
Warriors. Our time to conquer this planet and THE NEXT begins todeeeeeyy.
The world shall tremble at our war cry.
AND OUR WAR CRY IS SOI SOI SOI SOIIIIIIII SWEY
*Entire legion of necron warriors chanting SOI SOI SOI*
- Unnamed Necron Lord [[1]]

Necrons (Robo-Zombie Eygptians in SPEHSS) are one of the main factions in Warhammer 40,000. Basically, they're a bunch of soulless, skeletal, alien killing machines led by a robot aristocracy of angry murder machines and bound together by space-technology-magic (like atom-flaying weapons that strip their targets down into their constituent atoms).

Although they have been around since Rogue Trader (albeit only as a single picture categorized as an "unknown xenos species"), they have seen great change in almost every edition. In second edition, they were a mysterious faction with essentially zero fluff and only a few models, all of which looked incredibly silly, and Space Crusade introduced them as Chaos Androids (oh, the irony...). However, with third edition they got their own Codex and a bunch of models fleshing them out as an army and introducing their rulers, the C'tan (who were subsequently shoehorned into every major event in the 40k universe). Games Workshop then promptly forgot they existed and did not update them again until the closing days of fifth edition. This was a controversial move as the Codex was written by Matt Ward, who significantly changed the fluff, making them Newcrons. In short, they became Tomb Kings IN SPESS and the C'tan were demoted to being their bitches. And that's about it. Do note that although they are space Tomb Kings, they are not necessarily space Egyptians. Gameplay-wise, some used to consider the Necrons to have been unduly OP during their introduction. A respectable amount of evidence can be gathered to grant credence to this viewpoint based on the ease with which they can blow up vehicles using the basic Warrior's Gauss Flayer. The rapid change in fluff between the 5th edition codex and its predecessor is controversial, to put it lightly. While both versions of the Necrons' background have their fans, many would agree that the retconning was drastic and heavy-handed. On the one hand, the Necrons' theme used to be that they were emotionless, implacable alien killers led by Cthulhu-ish star gods that fed on people's souls. Their background was very sparse and included all sorts of mysterious things about the Necrons and the C'tan that had implications for the whole setting of Warhammer 40,000. The new codex gets rid of all the mystery and removes the dangerous feel the Necrons used to have in exchange for giving the individual Necron leaders and armies individual personality, which in turn allowed players to make their armies different. This was different from the previous situation where basically everyone had an army of similar silver OP doom warriors wielding guns that could rip through tanks as well as infantry and had over the top fluff that made them out to be the baddest sons of bitches in the galaxy.

The 7E Fluff in the codex is actually a lot more complex than those of prior codices with complete sections dedicated to paint schemes and analyses on the markings on them (Where the last edition only barely even begins with that) while also beginning to fluff out some of the more prominent dynasties. However, the not much of it actually changed from the last codex, so the C'tan-mon are still a thing (And are actually treated with less respect than even a warrior), as are eccentric, megalomaniacal undead robots.

Good news, everyone! With the Necrons now being somewhat popular, they are about to get a new slew of Forgeworld loving, thanks to the announcement that they are scheduled to be featured in Imperial Armor 12 along with the Minotaurs Chapter Space Marines (meaning we may finally get Medusa V Tomb Stalkers and Megaliths, so we don't have to rely on Pylon, Scarab, Barge, Warscythe, and Heat-ray spam to down Titans).

Apparently, 'Necron' is also the title of a bizarre and retarded fetish comic of some sort.

Reasons to NOT be a Necron

You're not Grimdark Machine Death March of Doom anymore.
- Well, maybe you are, depending on what Phaeron you serve. The Silent King's wimpy "let's all turn back into squishy mortals" whining only affects about half the Necrons.
You will be highly hated due to the amount of cheese in your units. Though this does have an allure of its own.
The Unholy Beast has handled your race with his touch. Although to your credit, the fluff isn't Ward Knights-tier terrible. At least we got Pokémon out of the deal. Right, guys? ... Guys?
You cannot differentiate the wimminz and the manz, so you will accept the risks.
- Unless you want to bang your leaders. Phaeron is the title for male Necrons, Phaerakh is the title for female Necrons.
Thanks to The Great Beast you can't be friends with Thomas Macabee anymore.
If you're an Oldcrons fan, you're never quite going to get the army you want because the C'tan have been glorified Pokémon for two whole editions and there's no signs of going back to the old fluff.

Novels and stories featuring the Necrons

Here is a list with a small synopsis of publications by Black Library and GeeDubs which feature them, before you start adding, remember, Necrons must not only be mentioned, but actually appear in the story, feel free to add new items and follow the alphabetic order:

Ambition Knows No Bounds: Rogue Trader trying to plunder a Necron Tomb World.
But Dust in the Wind: Imperial Fists vs Necrons, enuff said!
Cain's Last Stand: Chronologically the last novel of Commissar Ciaphas Cain, the Necrons appear later in the novel.
Caves of Ice: Cain and the Valhallan 597th are sent to an ice planet to defend a refinery from an ork horde, but an ugly surprise awaits below the installations.
Cold Steel: renegade imperial guard attempts to escape penal moon while there is a three-side war between the 'crons, space marines and khornates, featuring a Tesseract Vault.
Damnos: Ultramarines vs Necrons, features some Necrons POV, as well as the Ultramarines commanded by Cato Sicarius, if you don't like the Ultramarines, this may be the novel for you!
Dark Creed: Word Bearers vs Astartes Praeses, the Necrons come in the later part of the novel, a great portrayal of how they are actually totally scary and overpowered.
Dead Men Walking: Death-korps of Krieg vs Necrons, the novel has an extremely grim tone as it puts a lot of focus on the civilians caught in the campaign, and shows a lot of Krieg jerkassery, don't get too attached to any of the main characters and no Krieg-chan for you!
Echoes of the Tomb: One of the earliest novels of Ciaphas Cain, and the origin of his fear of the Necrons.
Hammer & Anvil: Sisters of Battle get slaughtered by the necrons and... wait! Are they fighting back? And they are actually competent? quite a nice read and gives the Sisters a lot of street creed back.
Imperial Armour Volume Twelve - The Fall of Orpheus: a Forgeworld book about the totally badass and horrifying Maynarkh Dynasty vs the Minotaurs and the Death-Korps of Krieg, overall an extremely cool, if expensive, book.
Infinite Circuit: A small story about a Cult Mechanicus procession getting their hands on a C'tan shard and the Deathwatch paying a visit to see what's going on.
Nightbringer: Ultramarines vs Dark Eldar and Human traitors rushing to get to the crypt of the Nightbringer, or perhaps it's just a shard.
Shield of Baal: Devourer: Necrons POV! Featuring Anrakyr the Traveler trying to seize a tomb-world and some Necron dynasty nobles trying to flee a Flayed-Ones overran crypt-complex, also, Blood Angels and Tyranids.
Shield of Baal: Exterminatus: campaign book featuring Anrakyr and the Mephrit Dynasty, teaming up with the Imperium to contain Hivefleet Leviathan, minimun oldcrons, maximun newcrons acting like Tomb Kings in space.
Spear of Macragge: Ultramarines tanks vs Necrons, as well as some Ultramarines internal politicking.
The Lords of Borsis: The preview for the World-Engine novel, featuring a Necron coup d'etat.
The Word of the Silent King: The Silent King himself dealing with the Blood Angels, it seems the old Necron monarch has been acquaintances with Sanguinius himself.
The World Engine: also known as ~~one of~~ the coolest Space Marines novel ever, it narrates the fight between the Astral Knights and the Necron dynasty from Borsis, if you liked the entry in the Codex, go for it!

Gallery

Suddenly, Monoliths just got even more awesome.
Angry Marines can really fuck your shit up.
Necron players are well-known for their carefully planned tactics of "move-shoot-move-shoot".
Thanks to Matt Ward this is now canon. Give thanks to our spiritual liege for Thaszar the Invincible!
IN THE GRIM DARKNESS OF THE 41ST MILLENNIUM, THE ARGUMENT STILL RAGES
Here we see the humble Lolcron, irritably drawing away.
Lolcron and lolicron - know the difference! Ya, ones a sex doll... Still tap dat ass though!
The funk of 40,000 years.
Lolcron is a lazy bum these days.
Necron update 2011 in a nutshell.
The Necron's ace in the hole.
Damn space commies.
Goddamnit.
Ah, the early weakling 5th-ed + OP 7th-ed buddies.
This is what we call a xeno double-down.
Monoliths are known to inspire great songs.
Flayed Ones are adept at finding ways to maintain a nice figure.
Phaeron Imotekh in all his egotistic glory.
[Spooky Scary Necrons, send shivers down your spine]
Hmmmm....What is taking Ol'Zandrekh so them long for our Necron flaying party?
C'tan-chan will suck your soul out through your urethra and she won't even touch your dick.
Go, Go, Necron Rangers...
Necrons in the galaxy
Necrons in the Segmentum Solar
Necrons in the Segmentum Obscurus
Necrons in the Segmentum Tempestus ‎
Necrons in the Northern Ultima Segmentum ‎
Necrons in the Southern Ultima Segmentum ‎
Necrons in the Segmentum Pacificus
Territory of the Sautekh Dynasty