The oldest of the known races in the galaxy, the Necrons have been lying dormant since dinosaurs still roamed Terra. A race of robotic skeletons created by the Star Gods known as the C'tan, they are now beginning to wake once more from their stasis.
Driven by a hatred for an ancient Xenos race known as the Old Ones, the Necrontyr made a deal with the C'tan to give up their physical bodies in order to become more powerful. This backfired on them however, as bereft of their physical form, the Necrons as they were now known, also became ruthless killing machines, unable to feel compassion.
After winning the War in Heaven against the Old Ones with the aid of the C'tan, the Silent King of the Necrons, Szarekh, turned on his former allies. Splitting them into thousands of shards, and binding each of these shards in a Tesseract Labyrinth, the Necrons now held power over the C'tan.
Their war won, and the galaxy in ruins, the Necrons began their Great Sleep. Szarekh took a ship into the intergalactic void, looking for redemption for the curse he had placed on his people. But now, word of the Silent King's return has been heard...
Within Warhammer 40k, the Necrons are a fairly resilient army, with the ability to bring back fallen warriors as their repair protocols kick into action. With technology far beyond the crude weaponry of the Imperium, and even beyond that of the ancient Aeldari races, there's little armour can do to stop them as their weaponry flays the flesh from bones in an instant.
Necrons are a great army to paint as a beginner, as their body is largely a single colour, and can therefore be made to look good with relatively little effort. For more experienced hobbyists, extra care and attention can be paid to the vehicles, which lend themselves well to the technique of edge highlighting.