As written in the Khala and as practiced by the Protoss on Aiur, on Shakuras after the evacuation of Aiur, in the Protoss Enclave, and on most surviving Protoss colonies, the Khalai represent the largest, most skilled, but least powerful of all the castes. The Khalai caste represents the entire Protoss’ population that is not in the Judicator or Templar castes, they are the engineers, scientists, teachers, farmers, construction works, and doctors for the Protoss, just to name a few of their roles in Protoss society.
Following the end of the Aeon of Strike, the Khalai caste rose to prominence with each new scientific discovery. It was members of the Khalai caste that first used the Khaydarin Crystals as a source of energy, it was also the Khalai caste that designed and built the first Nexus Pyramid that allowed the Protoss to explore other dimensions and spread their presence throughout the megaverse. It is also the Khalai caste that was stuck between the Judicator and the Templar castes during the final days of the Zerg invasion of Aiur. When the two other castes began to fight on Shakuras, it was also the Khalai caste that threw their lot in with the Judicator Enforcer Aldaris to prevent the Templar caste from destroying the Khala and their place in it.
The Khalai are very important to the Protoss race, as neither the Judicator caste, nor the Templar caste can truly repair or design the equipment they use. Through centuries of selective reproduction and breeding, the Khalai consists of highly skilled and intelligent Protoss. The Protoss within the Khalai caste are allowed to freely choose what they want to do and how to live their lives, and many find ways to remain in the Khalai caste but still join the military or perform administrative functions.