The Death Saurer was first recognized by Fine, who regained memories of the Zoid after touching a piece of stone tablet from the Garil Plateau ruins. This was our first look into its modern recognition, but stories of it survived the Ancient Zoidian race, with Dr. D recognizing old meurals of it. When the Geno Saurer first appeared, its foot steps were theorized to possibly be from the Death Saurer, though this turned out not to be the case.
The Death Saurer remained in production for some time, resurrected by Prozen, who'd taken over numerous ruins to learn more about the Ancient Zoidian people. It was created using the zoid gene element of the original, ancient Zoid. For the purpose of its development, he created the Geno Saurer using the Death Saurer's genetics, and gave the Zoid to Raven. He used them to gather countless Zoid cores, taking any target of opportunity, to add to the incubation chamber of the Death Saurer, presumeably to help it grow (though the reason isn't clarified.)
It wasn't until Fine arrived at the ruin, accompanied by Bang, that the Zoid finally stirred. It wasn't anticipated to wake up for some time, but Prozen recognized immediately that it was reacting to the presence of an Ancient Zoidian. He captured Fine, and took her into the ruin. She was rescued by Bang and the Blade Liger before he could realize whatever plans he'd been formulating. On their exit, the Death Saurer broke out of its containment, awakening with a hateful roar. Its particle cannon activated and it burned away all of the imperial Zoids protecting the ruin. Bang and Fine escaped in time, and soon after the Death Saurer settled back down, and was transported to a second laboratory.
Prozen used his coronation ceremony to encite the people against the Republic, but his words quickly fell apart as he brought the Death Saurer to the stage. The battle that ensued resulted in him destroying much of Guygalos, and with many Imperial Zoids standing in defense of Prince Rudolph's rightful rulership, the particle cannon was used to destroy indiscriminately. During this time, the Death Saurer was commanded by Prozen, not from the cockpit but from its shoulder. Bang Freiheit and his Blade Liger were used to punch through the Zoid Core, and subsequently through the Particle Intake Fan, causing the Zoid to detonate.
In the past, the Ancient Zoidian people used the Zoid Eve to produce countless Zoid cores, creating a world of limitless proserity and potential. Some Zoidians, however, used Zoids as weapons in their meaningless power struggles. The Zoids became so accustomed to combat after discovering their true warrior nature that they continued to fight even without objective. In order to put an end to these battles, the Ancient Zoidians created the Death Saurer. Even so, this was considered their biggest mistake. The incredible Zoid wiped out all civilizations on the planet, and almost drove the Zoidian people to extinction.
In an effort to stop its reign of destruction, a few of the remaining survivors tried to terminate the Zoid Eve, believing that all Zoids would cease to live at the same time as its destruction. Yet, they couldn't bring themselves to completely extinguish its power, which led to Zoids continuing to exist on Planet Zi. It's implied that the Eve still functioned at a reduced power, and that this inhibited Zoids ability to reproduce, even if not cutting it off entirely. Rather, it's clarified that if Eve were to awaken, they could reproduce limitlessly.
While they failed to shut down Zoid Eve, the problem of the Death Saurer still persisted. So, those who still live made one final effort to stop its reign of terror. They developed two ultra-violent scorpion-type Zoids, which presumeably were finally able to defeat the Death Saurer. This effort ended in the Death Saurer being sealed within a giant, reflective tab next to the Zoid Eve.
After the death of the cloned Death Saurer, Prozen was melded into its core to become an immorphous form of the core. He began to recognize himself as The Dark Kaiser, and believed he had transcended into a greater being. He began working with Hiltz and Rease towards a common goal; allegedly to revive the Zoid Eve, though each of them seemed to have their own ambitions and perspective.
Though they acted subserviant to The Dark Kaiser, when the time came for him to actually become the Death Saurer, the immorphous structure that had been its core instead absorbed the man, Prozen, and became a solid core once more. It fused to the core of the revived Death Saurer, and rejoined the body of the Ultimate Death Saurer, awakening the beast and allowing it to break its bindings. Hiltz, who had been absorbed into the Death Stinger core before this fusion, stated that Prozen had only been a means to an end, that the Death Saurer had used him to fulfill a higher purpose. That he was to be a "ghost body" to protect its Zoid Core until the time came. He asserted that only an Ancient Zoidian could control the Death Saurer, and his body rose to the surface of the once-again-immorphous core to control the final beast.
Almost as soon as the Death Saurer awoke, the gravity cannon of the Ultra Saurus was fired to end the Zoid. Unfortunately, the Death Saurer recognized this threat before the shot was fired, and struck the Ultra in the chest with a particle cannon. The subsequent gravity bullet was then compressed into a hyper gravity field, that the Death Saurer used to divide its particle beam across the globe, causing mass devastation.
It was also soon discovered that the Death Saurer had an armor-tight energy shield just like the Death Stinger. Thus far, none of the armies had been able to damage it, and with its destruction an immediate concern, the decision was made to shut down Zoid Eve. Fine was prepared to make that sacrifice, believing it was what should've been done in the past, but Bang interrupted at the last second. He came up with a new plan. To fire the Blade Liger out of the Gravity Cannon.
This absurd notion gave the Blade Liger the force it needed to punch through the tougher armor of the Death Saurer. Though the massive Zoid fired its particle cannon to intercept this attack, the Liger's shield was able to neutralize the particles enough to still land the hit. With the Zoid Core punched through, the Death Saurer collapsed, and its head was crushed by the falling rubble of Eveopolis, which sunk back into the earth.