- A protoss battlecry(src)
Aiur is the protoss homeworld, located in a star system with a single yellow star and possessing a single moon not unlike Luna. It is at least the third of the system's terrestrial planets, if not further out.
A great psionic matrix emanated from Aiur. Protoss structures and units, to a lesser extent, drew their energy from it. A nexus provided a link to this matrix, but pylons were needed to actually tap into the energy required to provide psionic energy to new colonies.
Aiur possesses great, almost spiritual significance to all protoss.
Aiur's moderate greenhouse-gas levels and low orbital eccentricity allowed it to develop a climate conducive to life. Over the eons, its humid rainforests teemed with a variety of species, the most advanced of which were the protoss, whose evolution was accelerated by the xel'naga. In addition to digging vast subterranean caverns, the xel'naga constructed a temple to mark the site where they first set foot upon Aiur.
The xel'naga eventually left Aiur due to growing antagonism among the protoss that led them to forget how to attune themselves to their primal psychic link. This led to the Aeon of Strife, during which Aiur's greater landmasses were devastated and many of its lesser life-forms were pushed to the brink of extinction.
Eventually, Khas unearthed khaydarin crystals left behind by the xel'naga. He channeled their primal energies through himself and rediscovered the communal psionic bond of the protoss. Khas revitalized protoss society through the Khala, which called upon the protoss to forgo their old feuds and reunite. Gradually, the protoss embraced their psychic link and were flooded with the thoughts, emotions, and experiences felt by every protoss.
The following centuries saw a golden age on Aiur. Its war-torn continents were healed; its native species flourished; and five cities and thirty-eight temples were erected across its surface. The protoss population swelled to billions, and Aiur became the hub of the Protoss Empire.
A group of rogue protoss shunned the Khala. The Conclave ordered Adun to eradicate them, but instead he attempted to convince them of the Khala's truth by teaching them how to manipulate their own latent psionic powers. Without the Khala's discipline, their powers spiraled out of control and unleashed psionic storms across Aiur. The Conclave banished the rogues from Aiur and they became known as the Dark Templar.
In 2500, the zerg launched a full-scale invasion of Aiur. The protoss defenders were overrun and countless zerg carved swaths of destruction across Aiur's continents. They seized the khaydarin crystals and destroyed the xel'naga temple before setting the khaydarin crystal in its place, allowing the Overmind to embed itself in Aiur's surface.
Praetor Fenix fought against the zerg but was hampered by the ability of their cerebrates to reincarnate. He was also held back by the incompetent leadership of the Conclave, the protoss governing body.
When former Executor Tassadar, a veteran of previous battles of the zerg who had turned rebel, returned to Aiur with Dark Prelate Zeratul, Judicator Aldaris attempted to arrest them. Tassadar's followers destroyed the Heart of the Conclave.
With the help of the renegade terrans of Raynor's Raiders, Tassadar and his followers weakened the Overmind, sustaining heavy losses in the process. Tassadar channeled Dark Templar energies through the hull of the Gantrithor and steered it on a collision course with the Overmind, destroying it. However, the zerg invasion left much of Aiur in ruins. The Conclave and nearly seventy percent of the population was killed. Aldaris, Fenix, Zeratul and Commander Jim Raynor banded together in order to unite and lead the scattered survivors, but the zerg continued to slaughter every protoss they encountered.
At Zeratul's suggestion, the Khalai survivors retreated to their last functional warp gate, fighting through a sizable zerg force to get there. Fenix and Raynor held back and protected their flank while the Khalai survivors escaped to Shakuras. Hundreds of thousands of protoss died during the evacuation. Some protoss were stranded on Aiur, and some observers remained behind to keep watch.
The zerg took control of the gate, but Raynor and Fenix retook it and shut it down to prevent the zerg from sending more reinforcements to Shakuras. Praetor Artanis sent though all the troops he could spare.
After being contacted by Sarah Kerrigan, Raynor brought Emperor Arcturus Mengsk, fleeing from the United Earth Directorate, to Aiur. The warp gate was activated and Fenix's troops held off the zerg who were incited to attack by its energies. Raynor's command center was destroyed by UED troops, but Lieutenant Samir Duran, supposedly a UED colonial officer, moved his forces out of place and the zerg intervened, allowing Mengsk and Raynor to escape through the warp gate while the UED retreated.
The protoss refugees on Shakuras made at least one trip to Aiur to recover wounded protoss warriors. Protoss commanders noticed stranded protoss but, believing they could not be rescued, kept their existence secret.
Around 2503, the zerg occupiers had stopped fighting each other, but had stopped spawning and continued to wander the planet like "discarded tools".
The stranded protoss divided into two factions—Shel'na Kryhas and Tal'darim— and clung to life on the ruined world, fighting and avoiding conflict with the zerg. The arrival of a preserver, contained within the brain of terran archaeologist Jake Ramsey, brought great changes to both groups of protoss. The former attempted to flee through the disabled (and then repaired) warp gate, while the latter splintered as they learned the truth behind their mysterious Benefactor. The Shel'na Kryhas and renegade Tal'darim banded together to attack the Benefactor, most giving up their lives using a powerful psionic technique to hold the Benefactor off.
Some of the renegade Tal'darim escaped but none of the Shel'na Kryhas made it. The remaining Tal'darim were attacked by zerg forces led by Ethan Stewart, who was seeking to use the gate and then find Ulrezaj. Ulrezaj absorbed some of his own followers to recharge his power before leaving in a xel'naga vessel, pursued by the zerg and Dominion.
Aiur came under Kerrigan's control. Although some areas were left untouched by the invasion, much of Aiur became a zerg breeding ground littered with ash, broken war machines, and the remains of the dead. A small number of protoss speculated that some of Aiur's other life-forms had been assimilated by the zerg and mutated into killing machines to serve the Swarm.
This article or section contains information about StarCraft: Ghost, which has been declared non-canon. Elements may be taken as 'flavor lore' however.
Echoes of the FutureEdit
In 2504, Zeratul returned to Aiur to learn the Overmind's secrets by making contact with the tendrils connected directly to its cortex. There he encountered the spirit of Tassadar, who revealed that the directive to destroy the protoss was forced upon the zerg and that Kerrigan was the only one who could free the zerg from slavery.
In 2506, the Daelaam launched an invasion of Aiur via the Golden Armada in an effort to retake it for the protoss. By this stage, the zerg were feral, and no longer under Kerrigan's control. At least one beachhead was established on the planet's surface, as the protoss came under attack by the zerg. They were able to hold off the creatures long enough for a pylon to be established, which allowed zealots to warp in and engage the zerg with more equitable numbers.
As the invasion progressed, a massive protoss army landed outside Kherrisan and pummeled its way in, reactivating the warp conduits present. However, upon reaching the last conduit the Protoss encountered hybrid resistance, revealing themselves as being the ones leading the broods on Aiur.  Hierarch Artanis, disturbed by this, sought Zeratul's guidance, who had attempted to warn him earlier about the coming of the fallen xel'naga Amon. He dispatched Zeratul to retrieve the Keystone from Korhal, which prophecy stated would be the salvation of the protoss. However, Zeratul found the Void Seeker destroyed. After reaching a nearby base, Executor Selendis reported she couldn't sense Artanis in the Khala anymore, an impossibility unless he had died.
Zeratul sent forces through the zerg hives to reach Artanis's last position, but encountered crazed Khalai protoss who attacked him. After reaching their base and clearing it of hostile protoss, Zeratul lost contact with Selendis. Amon revealed himself, stating he had taken control of all protoss within the Khala. The Nerazim, with no connection, were immune to his control, and Zeratul pushed his way to Artanis. Amon took direct control of the Hierarch, and Zeratul fought to cut Artanis's nerve chord and release him from Amon's control. Zeratul was successful, but not before Artanis landed a killing blow on him. In his last moments, Zeratul told Artanis to awaken the xel'naga and save their people.
Artanis, now freed, severed the cords of as many protoss as he could and met with Phasesmith Karax. The two, with the few Khalai protoss rescued from the Khala corruption, pushed for the arkship, the Spear of Adun, buried beneath Khor-shakal. Amon's zerg forces, corrupted protoss and hybrid attempted to stop them, but the protoss were able to reactivate the generators for the arkship and escape the planet.
Meanwhile, Amon formed a new host body from the protoss under his control and the remains of the Overmind. He fortified Aiur with zerg and hybrid forces, and began reforming part of its landscape to be more like the Void.  He then sent the Golden Armada, now corrupted to his will, to begin assaulting the sector, including attacking the Terran Dominion.
Eventually, Hierarch Artanis returned, gathering the Nerazim, Purifiers and the Tal'darim death fleet under his command in an effort to defeat Amon on Aiur. His first priority was to destroy the psionic matrix to delay the corrupted Golden Armada from pulling back to defend the planet. Highlord Alarak and Matriarch Vorazun destroyed the khaydarin crystal in Antioch, while Karax and Talandar destroyed the one in the temple grounds. Artanis and a unified Daelaam force destroyed the final crystal in the xel'naga caverns, delaying the Golden Armada's arrival. 
Using this time to their advantage, the Daelaam assaulted Amon's host body directly. They destroyed the Void shards shielding his body and reforming the land into a Void-like landscape. When the last shard was destroyed, Amon's host body awoke, but the combined Daelaam fleet unleashed a massive orbital bombardment that destroyed the host body.
Amon's conciousness remained within the Khala however, and Artanis fortified his position while he charged the Keystone, intending to pull Amon's consciousness into it. The Daelaam defenses held out against the zerg and hybrid attack waves, but eventually the Golden Armada arrived, attacking the Spear of Adun in orbit and besieging the Daelaam's lines. However, it was not enough to break through, and the Keystone activated, temporarily purging Amon from the Khala-bound protoss. They cut their nerve chords, and after Amon broke free of the Keystone he had no host left to inhabit, and was thus forced back into the Void.
A New UnityEdit
"Then we shall build a better one on top of it!"
With Aiur purged of both Amon and the zerg, the protoss had finally reclaimed their homeworld. Artanis visited the grave of Zeratul, putting his warp blade on top of it and attributing their victory to him. He swore he would build a new protoss civilization, unified by more than just the Khala.
Cities began to be rebuilt on the surface of Aiur, with structure of both Khalai and Nerazim architecture.
Aiur is a planet high in biodiversity and has a large variety of flora and fauna. Known species include;
- Crab beetle
- At least one species of bird
- Various aquatic species about the size of leeches.
- Aldera (destroyed)
- Kherrisan (destroyed)
- Khor-shakal (fortress city, destroyed)
- Mendella (ruins, replaced by a proving ground)
- Brushfire Island
- Cave of Relics
- Eldritch Lake
- Garden of Aiur
- River of Light
- Road of Remembrance
- Shreka Hills
- In the StarCraft II map editor, there exists a map of Aiur, showing the spread of creep across its surface. However, apart from the creep spread, this map is identical to one of Bel'Shir, so assessing its validity is difficult.
- The planet appears as a contestable territory in RISK: StarCraft.
- Aiur is erroneously shown to have three moons in the ending cinematic for the main Legacy of the Void campaign.