Xel'naga

The Xel'Naga are an ancient, cosmic race. The Xel'Naga helped the Protoss and the Zerg races to evolve. In the end, the Xel'Naga were nearly destroyed by their own creation, the Zerg, when the Zerg Overmind launched an attack against them from the planet Zerus. There are vague references to them assisting other races, possibly even Terrans, to reach a higher level in their individual evolutions.

History
The Xel'Naga came from beyond the Milky Way Galaxy, and were a psionically-attuned and highly advanced race. They had reached the ultimate stage of evolution and helped younger races evolve.

The Xel'Naga's primary intent was to engineer a being that possessed purity of essence and purity of form, and to this end they travelled the galaxy, altering many interesting species they had encountered. However, each time they met with failure.

Involvement with the Protoss
The Xel'Naga journeyed to the edge of the galaxy and to the huge engineered world of Aiur. Upon this world they discovered a psionic hunter race which would be known as the Protoss, who displayed amazing strength, speed and resilience. The Xel'Naga took this to be a sign of purity of form. The species also had a unique psionic link. Seeing them as a successful creation, they were named Protoss, meaning "first-born". The Xel'Naga secretly cared for them, and eventually, when they deemed it ready, revealed themselves to them. The site where they first set foot on Aiur was marked by a Temple which they constructed, over a nexus of cosmic energy.

The Protoss united, fascinated by these new "gods." They called the Xel'Naga the Ihan-rii, and also called them the "Great Teachers", the "Makers", and the "Guardians". The Protoss Tribe that grew closest to the Xel'Naga during this time was the Shelak Tribe. During this period the Protoss underwent rapid technological uplift. Eventually, however, splits developed among the tribes as they struggled on decisions of what they should think of the Xel'Naga. The Xel'Naga had worked to unite them in one organization, but instead the tribes split and distanced themselves from each other. Indeed, the split was so severe it caused the disappearance of the psionic link. The Xel'Naga, knowing that they had pushed their creation too far too fast, set off from Aiur disappointed at their failure. The Protoss, who felt betrayed, attacked the retreating Xel'Naga, killing hundreds. The majority of the Xel'Naga fleet sadly left Aiur and the Protoss behind.

The Protoss, left behind, had only themselves to turn upon, and suffered a kind of madness. This led to a stage of Protoss history called the Aeon of Strife.

The New Beginning

 * Main article: The New Beginning

A Protoss mystic named Savassan, from the Shelak Tribe, discovered the Khaydarin Crystals in a hidden Xel'Naga-crafted chamber on Aiur. With their power, he was able to slowly recreate the Protoss psychic link. In addition, he searched for other Xel'Naga caches, discovering a large underground city which had been built by the Xel'Naga.

Within the city, Savassan and his companion, Telmaar, discovered several dessciated "dead" Protoss, all from different Tribes, connected by organic wires to a very large crystal.

Savassan attached himself to the vines, and immediately began to wither, resembling the other "dead" Protoss. Telmaar quickly used the console to free Savassan, who immediately began to heal, phsysically and mentally. Savassan said he and the crystal "shared things" and now he knew the path to healing. He learned that the Ihan-rii should be referred to as "Xel'Naga" and told Telmaar that "we don't need the Xel'Naga, we only need each other".

The Protoss hated each other for driving the Xel'Naga away, but the real problem was hating their own flaws which had caused the loss of their communal link in the first place. Re-creating the link across the entire species would heal the madness and end the Strife, causing the Protoss to feel each others' emotions. He called this theory the Khala.

Savassan, later known as Khas, traveled throughout the Protoss settlements, introducing the Protoss to the theory of the Khala. This brought about the end of the Aeon of Strife.

Involvement with the Zerg
Having failed to create a race with the purity of form, the Xel'Naga now set out to create a race displaying only a purity of essence.

The Xel'Naga settled on an ash-world named Zerus located in the core of the galaxy, and chose the most insignificant lifeform upon the planet, a larval creature known as the Zerg. While having no ability to affect their physical surroundings, the Zerg had just the traits the Xel'Naga were looking for: genetic versatility and psionic sensitivity. They nurtured these creatures, allowing them to affect their surroundings in almost parasitic ways. Eventually, they began infesting the creatures of the planet, turning them into monstrosities. The Zerg spread rapidly across the planet, infesting or slaying every living lifeform on the surface. In addition to this, they would absorb the creature into their gene pool, allowing the Zerg to replicate and then duplicate them, fueling their rapid growth. The Xel'Naga realized their mistake with the Protoss so instead of revealing themselves, the Xel'Naga created something to speak for them and contain their collected instincts and sentience. The Overmind was created in the Xel'Naga's fashion to watch over the swarm. The Xel'Naga wanted to centralize the intelligence in the Overmind as opposed to the entire species, like they did with the Protoss. The Overmind, however, was plotting to destroy its creators and spread across the galaxy. A surprise attack was launched against the Xel'Naga, wiping out most of the race's Worldships and the greater whole of the Xel'Naga in the first waves. The ancient ones attempted to flee, but since the Zerg had been able to infest a spaceborne creature, capable of living and thriving in space, they were able to overrun the Xel'Naga Worldships with frightening ferocity and swiftness &mdash; consuming their knowledge and eventually leading them onto their eternal journey to the Protoss homeworld of Aiur.

Legacies

 * Main article: Xel'Naga Temple

The Xel'Naga have left behind many legacies. On a nexus of cosmic energy on Aiur, they built a Temple to mark the spot where they first set foot upon Aiur.

The Xel'Naga left a temple on Shakuras, also sitting on a nexus of cosmic energy, where their marks (such as darkening the planet and a temple capable of mass destruction) are more obvious. Finally, there are prophecies relating to the planet Braken, a Protoss world with religious significance.

The prophecies claim that "he who harnesses this world will someday wield great a power, sanctified by the ancient ones". This could be a reference to the Xel'Naga.

Ara'dor
The Xel'Naga used a "universal natural" code they termed "ara'dor", which means "perfect ratio". Terrans call it the Golden Mean, symbolized by Φ or φ ("phi").

In mathematics and the arts, two quantities are in the golden ratio if the ratio between the sum of those quantities and the larger one is the same as the ratio between the larger one and the smaller. The golden ratio is approximately 1.6180339887. The golden ratio is related to the Fibonacci sequence and the Golden Spiral.

An extinct race?
Only ruins remain, some functional, of the ancient race. It is possible that the Xel'Naga still live isolated on an unknown planet, that a few survivors of the doomed race managed to escape the wrath of the Zerg and thrive upon a distant world, cutting themselves off from outside contact (only the "greater whole" of the Xel'Naga were destroyed). If this is so, then it has not yet been discovered. To this day, the Protoss continue to carry on the legacy that is the Xel'Naga.

It is possible that Samir Duran is a Xel'Naga. During a hidden mission in the StarCraft: Brood War expansion set, he can be heard saying that he is a servant of a "far greater power" that has slept for countless ages, and is reflected by the Zerg-Protoss Hybrid within the mission's Stasis Cell. It can be assumed that he works for the Xel'Naga unless he is speaking in a sort of third person (or, perhaps, unless the Xel'Naga are themselves servants of another, unidentified entity). Both species that make up the Hybrid were considered semi-successful, and what would be better than to combine the purity of form and individual strength of the Protoss with the purity of essence and unity of the Zerg? Note that the Xel'Naga preferred to work behind the curtains (the Protoss being an exception). It would make sense to send an agent to do their work, and his ability to resist Zerg control and infiltrate the Terran ranks seems too astounding for a human, and his claim to have "had many names throughout the millenia," if accurate, is strong evidence against him being Human or even Protoss (none of whom, excepting Taldarin who survived in stasis, are claimed to have lived for multiple "millenia").

Blizzard Entertainment has suggested that the Xel'Naga will make an appearance of some kind in StarCraft II.