The Nathema Zealots were a group of powerful Force-sensitives under the command of, and founded by, Emperor Valkorion of the Eternal Empire. The Nathema Zealots were among the only Force-sensitive beings able to withstand the horrors of the Void through a regime of daily and intense rituals and meditation.
Through this mental conditioning, it allowed them to focus their power well, whilst at the same time eroding their free will, allowing Valkorion to create a completely subservient army of powerful Force users. However, such power came at another cost. During the conditioning, an unexpected side effect was found. Because of their adaptation to the Void, they started to become dependent on it for their own existence. Leaving Nathema would result in the Zealot falling into a catatonic state.
In an attempt to make use of what he dubbed a failed experiment, Emperor Valkorion redesigned the Zealots to act as an elite guard - the wardens for the prisoners he had sent to Nathema's Sanitarium. This included the Emperor's own daughter, Vaylin, who was the subject of a ritual designed to break her spirit and condition her mind.
When Senya Tirall infiltrated the facility where Vaylin was being held and attempted to take her daughter with her, six Nathema Zealots in their characteristic black armor and robes stood on a bridge in an attempt to stop her escape. Senya faced them with her lightsaber pike and defeated all six of them, even using their own yellow-bladed lightsabers against them. However, when Vaylin refused to leave with her mother, several more Zealots emerged from the Sanitarium with Valkorion to reclaim his daughter.
After Vaylin returned to Zakuul, the Sanitarium fell into disuse, though the Nathema Zealots remained. Some years later, Vaylin returned to the Sanitarium to undergo a dangerous treatment that would remove her conditioning. The Zealots assisted the Jarak and the Keepers in their preparations for the treatment. Shortly after Vaylin arrived, the Outlander and Lana Beniko stormed the Sanitarium and engaged those Zealots not occupied with Vaylin. When the true depths of Vaylin's power were finally unleashed, the Zealots present fled the exploding machinery and the death cloud that she had unleashed. Now in full control of her powers, Vaylin returned to her fleet and ordered the destruction of the Sanitarium, likely destroying the last of the Nathema Zealots.