Juras was the conceptual designer of the motherships that were launched to explore the galaxy in the Golden Age of Expansion. While the motherships bore his design, the Templar Caste, against his objections, installed weapons systems on them, even converting some of the vessels to lead armadas. Juras was still allowed to keep his prototype ship, the Moratun, for exploration however.
Juras was among the researchers studying the kalathi when they broke out into civil war. Juras suggested using a "mighty weapon" of his design to scare the kalathi into ending their war. However, the kalathi were enraged and tried to kill the researchers instead. The weapon was used to kill them. The kalathi continued to attack the protoss, until they were decimated by colossi. Juras was profoundly affected by the incident, having witnessed the destruction of kalathi and their great city. This started his pacifism.
Juras would later be put into stasis alone on the Moratun, intending to awaken when the protoss made first contact with other sentient life, therefore spurring another renaissance of art and culture. Juras believed any sentient species advanced enough to achieve spaceflight would be driven by the need to reach out, learn and share with others. He refused to use protoss weapons against any other sentience.
Upon the Fall of Aiur, the protoss summoned the dormant motherships to Aiur with the message "we are lost", waking Juras. He was subject to the unpleasant feeling of waking up from stasis. During the journey, the Moratun warped to Samiku, a protoss colony, for a course correction and to pick up crew.
Juras observed out-of-control zerg overrunning the colony and killing zealots. Juras made contact with the zealots' commander, Martul. He was initially unwilling to kill the zerg, feeling it wasn't right to slay sentience, but he didn't want to allow the protoss to die, and the zerg had already been cut off from their "guiding intelligence" so Juras believed that killing them would be a blessing to the zerg. The Moratun destroyed numerous zerg and transported the zealots aboard. Juras refused to engage any more zerg, telling Martul he would return to Aiur, learn about the zerg, and seek the advice of the Conclave. Martul, in turn, threatened to take control of the Moratun from Juras and accused him of madness.
Near Aiur, the mothership's passengers felt uneasy due to the devastation of Aiur. Juras and Martul continued to disagree on the proper course of action. As they flew through a cloud layer, the zerg attacked, but Juras refused to fire back and locked the weapons system, even when Martul threatened his life. However, he changed his mind upon seeing the zerg butcher a helpless member of the Khalai Caste; a protoss noncombatant. Finally understanding the zerg's savage nature, Juras activated the mothership's special weapons systems—including the vortex, the temporal rift, and the wormhole transit—and allowed the zealots to operate the weapons systems to kill the zerg.
Other empty motherships had arrived; Juras, having rescued a few protoss from Aiur and other out-world garrisons, distributed them, along with the zealots he had rescued, among them. They were occasionally attacked by zerg leviathans but the motherships decimated them quickly. None of the survivors knew where the protoss had fled. Prior to death, a mortally wounded survivor told him that the refugees had found sanctuary with the Dark Templar. Juras intended to find them and deliver the motherships to be used solely for the destruction of the Zerg Swarm.