Ynnead

Ynnead looking like he's about to wreck Slaanesh's shit. Also has an uncanny resemblance to late musician David Bowie in Labyrinth.

OOOOOooooooOOOOoooooooOOOOoooo.....2Spoopy4Me.... - Ynnead pondering on his existence

“To the last, I grapple with thee; from hell's heart, I stab at thee; for hate's sake, I spit my last breath at thee”.
— Captain Ahab, Moby-Dick

Ynnead is the Eldar God of the Dead Voltron reincarnation of David Bowie (Ha! Bet you can't unsee that now!!!! (Cegorach pls)). Or at least he will be, as he is currently being created. He is in godly limbo at the moment as the Eldar try to amass enough pure souls, or at least desireless souls, in the various craftworlds' infinity circuits to give him enough mojo to become a proper god. Part of the problem with this is that each Craftworld's Infinity Circuit is separate from the rest, meaning the Eldar's goal has the massive flaw of not having the pieces together. The other problem that will probably backfire horribly in true 40k fashion is that the Eldar are all greedy, hyper hubris-filled, obsessed with eventually conquering the galaxy (while refusing to accept that squatting in their small patch of space for sixty million years does not make the galaxy theirs and is not the same as ruling the galaxy), jealous of the Imperium's rise and strength, and generally desire everything in the universe for themselves and desire to be free of their curse so they can go all Corsair on everyone for the lulz because they feel entitled to it. Now, considering how Slaanesh turned out from their bad habits, does this really seem like a good idea? On the other hand, the Eldar are probably going to get what is coming to them. Just not quite what they had expected or hoped for.

This is without getting into the supreme stupidity of attempting to send essentially a giant, ultra-powerful Eldar soul against a being which is not only intrinsically tied to all Eldar souls but also considers them to be a delicacy. For fuck's sake! Stupid damn space elves! You know, the definition of insanity? Doing the same thing over and over again yet expecting a different result.

The whole process of god creation is a bit of a tricky one to explain, but we'll try to keep it simple.

Basically, Ynnead is the Eldar's last hope against Slaanesh. When the bitch-goddess was born, she devoured most of the Eldar race, and their souls, and most of their gods, and basically caused a lot of things to get badly screwed up, making a terrible mess in the toilet afterwards that the Eldar where forced to mop up. The crap on the wall that won't scrub off was that the surviving Eldar found Slaanesh was constantly hungering for their souls, laying in wait for the moment when any member of their race died to completely consume them. In the past the Eldar believed that when they died, their soul would be reincarnated in the form of a Jokaero. With Slaanesh's coming though, the Eldar's ability to reincarnate disappeared.

To save themselves from this fate, the Craftworld Eldar use spiritstones to trap their souls upon death. The spiritstone is then used to inter the soul within the infinity circuit of a craftworld, next to a carefully placed egg timer, where the soul is free to roam around and commingle with the other Eldar souls of the craftworld.

As more souls over time have been added to the infinity circuits, the Eldar Farseers have perceived something stirring from this collection of souls; this is Ynnead, a god formed from untainted Eldar souls and the power of Asuryan, the king of the Eldar gods, who passed on his power to the Farseers of the Eldar before he was devoured by Slaanesh. The Farseers believe that when the last Craftworld Eldar dies, Ynnead will be fully born and will rise up to cast down Slaanesh, destroying him/her/it forever.

It's unknown whether this is feasible or not considering Slaanesh's immense power, but Ynnead is the Eldar race's last, best hope for a better future, and so all their efforts go towards making him as strong as possible. Plus, Khorne would probably jump at the chance to finally get rid of Slaanesh and its merry band of chickenshits once and for all, consequences be damned.

All of this assumes that Ynnead would give a shit about any of this, of course. The Eldar's past track record for creating gods makes it highly dubious that this one will turn out any better, and as far as anyone knows it could just make like Nagash and try to make itself a Chaos God instead.

The Star Child/Ynnead Theory

There is a theory stating that when the Emperor screwed Horus's soul to the wall, part of the Emperor's soul was also cast into the Warp. This Emprasoul fragment is the Star Child, another god waiting to be reborn—or perhaps to be reincarnated into human flesh. If the remains of the Emperor were ever to die, the tiny spark of soul left in his body would re-united with the greater whole, and according to prophecy, stalemate the four Chaos Gods while the races of the galaxy were left to battle it out in one last great Ragnarok scenario.

More recent (2006 onwards) fluff from Xenology grants some credence to this theory by suggesting an image of an "unborn child surrounded in starlight" as one of the three future survivors of the galaxy's conflicts (the others being Khaine and the Laughing God). While this may refer specifically to Ynnead, who is supposed to be born from the Webway when the last Eldar has died, it is now conceivable that Ynnead and the Emperor's star child are the same entity, particularly with the revelations in Horus Heresy that the Golden Throne is a (failed) doorway into the Webway itself.

This is made more relevant when you consider the fact that the Eldar Gods (the Old Ones) do not belong exclusively to the Eldar alone, and were active amongst several races all at the same time. So Ynnead does not have to be an "Eldar" god, just a powerful enough being to actually count as a god. The Emperor ticks that box, finally unifying the two species in the galaxy with the most in common, and, truth be told, the least reason to fight (except for the Dark Eldar).

On the other hand, the star child theory's biggest proponents proved to be cultists of Tzeentch, which makes it very likely that all of the above is completely untrue. So believe what you will, and always act on the assumption that most of it is wrong somehow.

The Gathering Storm

Ynnead is prematurely "born" during the 13th Black Crusade following the fall of Cadia. Eldrad Ulthran attempts to summon him early by stealing the fossilized bodies of all the dead Farseers of all the craftworlds and conducting an elaborate ritual on a crystal moon. It gets fucked up by the Deathwatch and only a tiny fraction of Ynnead enters the Materium.

After searching through space, this fragment discovers Yvraine, an Eldar who was originally a Dire Avenger from Biel-Tan that became a Warlock, then an Outcast, rose to become a Corsair captain only to lose her command in a mutiny, and ended up living and fighting in the slums of Commorragh, joining a Wych cult and then rising to Succubus. This makes her the ultimate expression of being Eldar because apparently the true Eldar are supposed to travel all the paths of life, even the dark ones. With her is the Visarch, a former Exarch of the Dire Avengers who trained Yvraine and had his heart broken when she chose to leave rather than succeed him. He ended up sneaking into Comorragh, pretended to be an Incubus, and fought his way to Yvraine after she unlocked the power of The Sword of Sorrows actually had one of the severed fingers of Morai-Heg forged into a sword by Vaul. The Visarch would later get his own sweet croneblade The Sword of Silence when it was pulled from the heart of Craftworld Biel-Tan.

Together, Yvraine and the Visarch become the prophets of Ynnead, preaching that not ALL the Eldar have to die for Ynnead to be born. This ends up fracturing Eldar society at all levels, and Biel-Tan ends up tearing itself apart over whether or not this is actually Eldar heresy. The destruction of Biel-Tan causes all kinds of Warp holes to tear themselves into existence around the ruins, and Ynnead births an Avatar through them known as the Yncarne (get the pun?), the one-horned ghost-fire model that's been making the rounds in photos of the latest White Dwarf.

Yvraine, Visarch, and Yncarne are now gathering an army of all the branches of the Eldar race who believe they can fight Chaos without all having to harakiri while those who don't believe in Ynnead are preparing to kill all the heretics for daring to alter the fate of the Eldar. Eldrad is himself imprisoned and placed on trial by the Eldar Inquisition, because he's not Eldar enough and proposed, after his failure to birth Ynnead, allying with the Imperium of Man to defeat Chaos once and for all. Even if the other Eldar don't like the idea of becoming best buddies with the Imperium, that didn't stop Yvraine from helping to resurrect Roboute Guilliman, so perhaps an actual alliance may be possible.

The Gods of the Eldar
Asuryan - Cegorach - Isha - Kurnous - Khaine - Lileath - Morai-Heg - Vaul - Ynnead