"He is the Breaker of Gods"
"He who knows, does not speak. He who speaks, does not know. "
- – Laozi, The Tao Te Ching
"The hardest choices require the strongest wills."
- – Thanos
The Silent King is the ruler of all Necrons, though in the 41st millennium his influence is starting to dwindle. Back when the Necrons were still the Necrontyr, it was a hereditary position occupied by the ruling member of the Triarch (which was itself composed of three Phaerons of powerful Dynasties). The name was derived from the tradition that the Silent King never spoke to his subjects, instead letting the other two Triarchs speak for him.
The big S.K. was intended to be a background "ghost" character; to reinforce this, GeeDubs deliberately withheld giving him his own model and rules for four entire editions...
Szarekh, The Last Silent King
The last Silent King was named Szarekh, and it was he who sealed the pact with the C'tan in order to gain their power to fight against the Old Ones. Unfortunately for the Necrontyr, there was a catch: the bio-transference process that upgraded them into the metallic, immortal Necrons had the side-effect of stripping them of their souls and, for the most part, their free wills. The Silent King was placed in charge of the entirety of the Necron race, while the delicious souls went to the C'tan.
Szarekh was not happy about this (though he wasn't precisely angry either, given the loss of his soul), but he had no leverage to fight the C'tan -- what they had given, they could easily take away, and then some. Therefore, he fought the War in Heaven alongside the C'tan, and waited until the very moment of victory, when the C'tan were nearly spent, and turned on them with every warrior and weapon at his disposal, shattering the star-gods and binding the fragments that remained.
The War in Heaven left the galaxy a mess, and Szarekh decided that most of it was his fault, so he commanded the legions to rest in their Tomb Worlds to let the galaxy heal for the next sixty million years, relinquished control of the Necron nobles, and exiled himself from the galaxy. His last instruction was to rebuild the Necrontyr Empire and return to flesh bodies, though how this happened was left up to any Phaerons who could make it happen. Szarekh then left for the intergalactic void, vowing to never return to the Milky Way...
...which lasted right up until he found out what was in the void: the Tyranids. When he encountered the vanguard of Hive Fleet Behemoth, he NOPE'd right back home, getting in touch with the remaining Praetorians to awaken every Tomb World still standing and unite against the swarm -- after all, if the Tyranids ate everything, there would be no bodies to return to, and nothing to rule over! The Silent King so disliked this possibility that he allied with the Blood Angels to fight off a Tyranid landing force, and even let them go on their way when the fighting was over.
He's back with the reveal of 9E. His new model even has a retinue, not unlike another influential bone-daddy and he even has a C'tan shard with him. His stands on top his personal pimp throne looking totes SWAG. It does NOT look happy with its current living conditions (It probably doesn't help that its heavily hinted that Szarekh is currently wearing its flayed skin as his cape).
During the Alliance negotiations with Dante, the Silent King mentioned a similar conversation with their Primarch, Sanguinius. This would mean that Szarekh had already returned 10,000 years before the 1st Tyrannic War and one of the Primarchs was aware of the Tyranid threat. Common sense dictates that this happened just before it all went to shit and all the humans involved got killed (or sat on the Golden Throne) before spreading the alarm.
Either that or he lied with help from his High Chronomancer. Just as planned.
Szarekh as a hero
Szarekh is one of the most interesting head figures in Warhammer 40k. Morally he is a very complex character. Whereas other heads of factions could be qualified as good people in terrible situations, such as Guilliman or Farsight, while others are definitely just evil people doing evil for the evulz, such as Vect or Abaddon. Szarekh is in a weird spot that leaves much of his morality up for interpretation depending on how you see his actions.
Szarekh's actions have both been tremendously evil, such as what he did to his own people turning them into Necrons, but also tremendously good, such as killing the C'tan and freeing his people from his own grip (like a certain someone also said he would do once humanity had evolved enough). Not only did he forsake power, but also out of guilt he left the galaxy. This does show some character development, more than most 40k characters get.
Then we don't know what he had been doing for 60 million years, it should be interesting to know what other galaxies think about the Silent King.
All we do know is that Szarekh came back, not just to save his people from the Tyranids, but to save most of the sentient life in the galaxy. And here is where motivation becomes extremely important to know where Szarekh lies within the moral spectrum.
You see the official reason why the Necrons are trying to save other sentient species from the Nids and the Great beast is supposedly to later see if it is possible to make some reverse biotransference, which should mean Szarekh's desire to save other races is fueled out of selfish motives.
But the Indomitus book offers a different possibility for the motivation within the Silent King's attempt to save other sentient species. The plasmancer says that Szarekh ordered his Nemesors to try to preserve human life if possible in order to "use them as labor" in case biotransference is not possible. Now think about it, using humans as labor is a terrible idea if you are a Necron. Necrons have drones in droves to do manual labor, so autonomous humans who need amenities and extensively processed biomatter are useless as a workforce to them. Yet Szarekh insists on telling the Necrons to preserve the life of these meatbags for two ultimately futile endeavors.
What if he is actually just trying to convince overlords to not kill sentient species by using these two motives as excuses to justify such an order?
Szarekh has clearly done horrible things, but it is entirely possible that he is trying to redeem himself for his actions, both towards his people and towards the galaxy. Or he is a lighter shade of grey, not-so-Grimdark imperialist who just wants to rule over as many diverse subjects as possible without being a murderous dick. Clearly the morality of Szarekh requires a lot more study within the black library, after all we don't see many great redemption arcs in Warhammer 40k, and Szarekh can provide us with one.