Death Metal Empire
The Death-Rex is a small Zoid with an open-air cockpit. Compared to other Zoids in the Zoids: Wild series, it is an XL-sized Zoid.
The Death Rex is part of the same legend that the Wild Liger is depicted in.
The Death Rex is piloted by Gallagher. It is a legendary Zoid that sits atop the food chain. It is said to be responsible for the extinction of half of all Zoids species.
The Death Rex is used by Gallgaher when not using his Gilraptor. It is a fearsome, nearly uncontrollable, so it is spent locked up nearly all the time.
It is revealed that in the past, Gallgaher and Bacon were once friends and trained under the same master. Gallgaher's lust for power, and inability to beat Bacon, led him to seek stronger and stronger Zoids. While Bacon partnered with the Fang Tiger, Gallgaher found the Death Rex.
The Death Rex first appears in episode 13, where it fights, and defeats, Bacon.
After the loss of Bacon, Team Supreme and Freedom ambush Gallagher in episode 20, and this is where Gallagher uses the Death Rex's Death Blast for the first time. It's proven to be nearly unbeatable, but also very unstable. The Death Metal Key used by Gallagher quickly disintegrates after using the Death Blast.
At the conclusion of the series, it's revealed that the Death Rex isn't evil per-se, merely that it's power is so great that it had been used for destruction. When the Death Rex is split up from Gallagher, Arashi nearly tries to coax the Death Rex out of it's Death Blast, but is ultimately unsuccessful. The Death Rex is shown falling into lava back at the site where it was first excavated.