Zeratul is a Dark Templar, a renowned psionic warrior and assassin whose forbears were exiled from the protoss homeworld of Aiur over a thousand years ago. The dark templar refused to submerge themselves in the communal protoss mind link, the Khala, preferring instead to strive as individuals. Zeratul holds the rank of prelate and is probably best known for his role in ensuring the survival of the protoss since the zerg threat first became apparent.
It was Zeratul who overcame the prejudices of Executor Tassadar when they met on Char and thus began to heal the rift between the Aiur protoss and the dark templar. It was Zeratul who was the first to slay a zerg cerebrate although the cerebrates had been thought immortal. Most of all it was Zeratul who returned to Aiur with Tassadar and set into motion the events that would rejoin the sundered halves of the protoss race and overthrow the oppressive rulership of the Conclave.
Zeratul went on to fight alongside Tassadar to bring about the destruction of the zerg Overmind during the invasion of Aiur, and then helped the protoss evacuate the planet as it continued to be overrun by the zerg. When the Swarm followed the refugees to the dark templar world of Shakuras, Zeratul helped recover the Khalis and Uraj crystals, which allowed the protoss to activate the xel’naga temple there and wipe out the invaders. Later, when the dark archon Ulrezaj threatened to destroy the Aiur protoss “violating” Shakuras, Zeratul was instrumental in thwarting Ulrezaj’s schemes.
But Zeratul also carries many terrible burdens. In the act of slaying the cerebrate Zasz, Zeratul became temporarily linked with the Overmind. Zeratul came to know much about the Overmind’s plans, but the zerg leader gleaned the location of Aiur itself from Zeratul’s mind, and so the seeds of the planet’s devastation were sown. Furthermore, Zeratul has a long and bitter history with the Queen of Blades, having been manipulated and betrayed by her more than once as she destroyed the remaining zerg cerebrates in order to secure her control over the Swarm after the Overmind’s death.
As part of her schemes, the Queen of Blades took control of the beloved protoss matriarch Raszagal. Zeratul later rescued the matriarch, but he found her to be irrevocably corrupted. Sorrowfully he took the matriarch’s life to spare her from continuing as the plaything of the Queen of Blades. With her mind freed by the deathblow, Raszagal thanked him and named him as leader of the dark templar. Such an honor Zeratul felt unfit to take, his soul too scarred by his experiences.
For the moment he focused on a more immediate concern: contacting any other nearby protoss who had survived the Queen of Blades’ treachery. Tracking protoss power signatures to an obscure moon, he hoped to reunite with his comrades and return to Shakuras with them in order to plan for the future. Instead of comrades, however, he found a former agent of the Queen of Blades – the enigmatic Samir Duran – engaged in breeding protoss/zerg hybrid creatures. Although Zeratul destroyed the facility, Duran claimed that it was merely one of many. Duran also revealed that he had been known by many names over the millennia and that he was not serving the Queen of Blades, but rather a “far greater power.” Deeply troubled by what he had seen, Zeratul went into self-imposed exile with only a handful of followers at his side. He continued to seek answers for what manner of being Duran truly was, and what dark future he was working toward. Initially distraught with his lack of progress, the urging of a terran archeologist Jake Ramsey and the protoss preserver Zamara pushed him toward uncovering the truth.
Through his quest, Zeratul uncovered a xel'naga prophecy, commands brought through time and space to help in a coming war against a fallen xel'naga named Amon. At the site of the dead Overmind, Zeratul received a vision from a xel'naga in the guise of the spirit that appeared as Tassadar, which required the survival of the one he hated most: Sarah Kerrigan. Abhorred, but knowing the universe was at stake, Zeratul delivered his knowledge of the prophecy to his old terran comrade Jim Raynor, pleading with him not to kill her for the sake of the universe. Such an act saved Kerrigan when Raynor purified her of her infestation, and Zeratul would later guide her to the zerg's birthworld of Zerus, seeing to turn her into primal zerg to give her the power she needed to face Amon without the taint of a race manipulated by him. With her guided, Zeratul then sought to find how the protoss fit into the grand scheme.
Zeratul sought answers from Duran's old terran bases (as he had been banished to the Void by Kerrigan), and with the aid of Praetor Talis, rescued protoss prisoners who were able to point them to the temple Amon was resurrected at. Zeratul and Talis attacked the planet and infiltrated the temple, where the Tassadar spirit again spoke to Zeratul, telling him that the Keystone, the relic the purified Kerrigan of her infestation, would usher them unto hope. Zeratul escaped the temple, though Talis gave her life in the process, and delivered the message to Artanis, though too late: Artanis had begun the reclamation of their homeworld of Aiur. However, the attack went awry as Amon's protoss/zerg hybrid were found to be commanding the feral zerg the infested the planet. Artanis then took Zeratul's warnings seriously, and prepared to fight the Keystone, when Amon siezed control of all protoss bound to the mind link of the Khala. Zeratul fought to sever Artanis from Amon's control, and after a clash of blades Zeratul successfully severd Artanis's nerve cord, but not before an Amon-posessed Artanis struck a killing blow on Zeratul. In his dying moments, Zeratul entrusted Artanis with the fight against Amon, a fight Artanis would win. The protoss would drive Amon back into the Void, and years later, a joint force would slay him once and for all. Zeratul's hunt for the truth would avert the end of creation, and put an end to the schemes of a mad god.
Artanis placed the Zeratul's warp blade on a lone grave on their reclaimed homeworld of Aiur, promising to create the united protoss civilization they had envisioned.