Not much of Luxaar's past is known although what is known is that he started the war that destroyed Earth. He intended to wipe out all of humanity with this war but 20 million humans escaped on the White Whale, the lone ship that managed to get past the war unscathed.
Xenoblade Chronicles X
Luxaar spends most of the time in the game inside the Ganglion ship issuing orders to the Ganglion and other races forced to work for the Ganglion such as the Prone, Mamuck and Wrothians. Also when ever one of his subordinates states that humans could be the fail safe of legend, he gets extremely angry and denies it.
However it is revealed in the final chapter that Luxaar made a deal with Lao, a BLADE, to destroy humanity. What Lao got out of the deal is unknown though Lao most likely agreed to death at the hands of the Ganglion.
During the final chapter it is revealed that both the Ganglion and the humans have located the Lifehold Core, the containment unit that contains all 20 million human consciences. If the unit goes offline every single human dies making this the most important battle since both races landed on Mira. The Ganglion get to the Core first but are stopped by a trion barrier. Elma's team head inside the core to reboot the system but are stopped by Luxaar who manages to get through the barrier using the Vita engaging in combat with the humans.
During the battle Luxaar reveals that the Ganglion are indeed fearful of humanity. He reveals that the samaarians came from another plane of existence and should the Ganglion turn against them they would be destroyed. He also reveals that he thought the Samaarians had been destroyed and yet here humanity is, the descendants of the Samaarians. He then executes the second form of the Vita to fight the humans.
The humans manage to destroy the Vita and celebrate their victory. However Luxaar remains alive and begins firing energy spheres at the computer inside the Core in a last ditch attempt to turn off the core and kill all 20 million humans. This action causes the Core to create biological weapons to defend itself. With attacks coming on both sides, the humans are destined to die until Lao appears backstabbing Luxaar.
As soon as the biological weapons are taken care of, the Vita starts to sink down into the protoplasm taking both Luxaar and Lao with it. Luxaar begins to dissolve into the protoplasm realizing that it is human DNA and that the legend was indeed true. Lao then emerges as a chimera having absorbed all kinds of DNA, including Luxaar's and engages Elma's team in combat. Halfway through the battle Lao reveals that Luxaar is a part of him now and that he retains Luxaar's memories. Lao reveals the reason the Ganglion feared humanity so much was because the Samaarians were the creators of the Ganglion. Elma's team destroys the chimera ending Luxaar once and for all. This also results in the destruction of the Ganglion army.
- Ironically Luxaar was the cause of his own demise. Had Luxaar continued his plans and not destroyed Earth in fear, humanity would not have landed on Mira and Luxaar could have used the Vita to revive the Great One as he intended to.