Terrex is a very powerful creature without a soul. Thus it serves as a host for any living organism who would like to meld with it. Terrex is born from Earth, he is a piece of our own world and have immense power:
It can do anything to a living creature, strenghten it, weaken it, renew it or even anihilate it. Touching him can be lethal.
Terrex was created by a scientist of Titan who intended to use it in case Thanos won the control of this planet. It was supposed to trigger doomsday. But the Mad Titan of Saturn managed to kill the scientist before he could activate this weapon and only Moondragon knew how to use it after him.
She brought Terrex on Earth, deceived by Kerwin J. Broderick, in his quest to become the king of San Francisco. Broderick melds with Terrex and Daredevil has to team up with Captain Marvel, Moondragon and Angar the Screamer in order to defeat Terrex by luring him into an illusion of un-life.