The Intruders are in actuality the equivalent of what a Traveler is and represents, but they herald from two "older" and completely different "Systems" that exist Beyond the Edge of Space. They have been summoned from their mother systems by the Elder Masters to come to the Glyos System and regain control.
The Elder Masters are near omnipotent in their scope and their vision, but cannot physically gain entry into the worlds that they create themselves. Therefore, their bidding is carried out by the "First Children", which began with the Kydrothi, the Waellex and the youngest of the trio, the Delphi. Each race was sent to a newborn system, charged with guiding and manipulating the lifeforms of each separate system according to the plans of the Elder Masters.
Only the Delphi dared to eventually rise against the harsh reign of the Elder Masters, rebelling when their own "children", the Armorvor, were ordered destroyed by the Elder Masters. Through the intermittent and unexplained appearance of the dimension bending Zorennor Rift, the Delphi found a way to hide their Armorvor from the vision of the Elder Masters, who somehow could not see into the Rift itself.
To replace the Delphi after their rebellion, the Elder Masters created the Traveler, a less powerful but more controllable race of beings than the three races of the First Children. Even though the Traveler race was intentionally designed to obey more easily than their predecessors, they began to also awaken to the cruelty of the Elder Masters, thanks to the intervention of the Delphi, who had become more powerful while within the Zorennor Rift, gaining a new mastery of time space through the use of forgotten Dimension Gate technology.