Gerhardt van Rijn was a terran scientist and the lab director of a research base on Vygoire. During their studies, the researchers came into contact with strange spores hat had psychoactive effects. They became intent on sacrificing themselves to the "Great One." van Rijn was intent (or claimed to be) on sacrificing himself as well, but only after all his "children" had been sacrificed beforehand. He claimed as such when he and his fellow survivors were confronted by a DMC platoon.
It was at this point that the ultralisk returned. In the chaos, some of the scientists began attempting to 'sacrifice' themselves. van Rijn ordered them to do so, but one at a time. For, as he explained to the marines when he and his other cultists joined them at the lab complex, a communion of more than one cultist at a time, was not a "pure" one. He went on to claim the marines' presence had riled the Great One, and it had become wanton in its hunger. He then led his cultists back into the jungle—the alignment of Vygoire's moons was at hand, as was the time of communion.
Torch Seven devised a plan to trap the Great One in a ravine, burying it under rubble using a vespene gas bomb. Van Rijn and his followers attempted to stop this in every way they could, but were easily shoved out of the way by the armored marines. The trap was set, and Doakes used the ceremony of the alignment of the moons to lure the Great One to him, and into the trap in the ravine. Torch Seven collapsed the rocks on top of the zerg beast, but that did not kill it. The Great One kept fighting, slaughtering both Torch Seven's marines and Van Rijn's cultists who willingly ran to be slaughtered by it. Doakes was smashed aside by the ultralisk, but managed to shove his rifle in one of the wounds on its leg, blasting it open. Van Rijn felt the pain of the beast, and ran toward it. He was sliced in half by its massive kaiser blades.