Stuff is a member of the Imperial Guard, a multi-ethnic group of super-powered alien beings who act as enforcers of the laws of the Shi'ar Empire. The shape-shifting amoeba-like Stuff was the advance scout for the Guard's first strike on the team of superhuman mutant adventurers known as the X-Men after the Shi'ar Empress Lilandra, under the mental control of Charles Xavier's mutant twin sister Cassandra Nova, had ordered the destruction of all mutants on Earth. Stuff had assumed the form of a Japanese human named Kato to infiltrate the X-Men's mansion headquarters and covertly gauge its defenses and the capabilities of its residents.
Following the initial attack by the rest of the Imperial Guard, Stuff's mind was taken over by the young telepathic trainees of the X-Man Emma Frost known as the Stepford Cuckoos. Together, the telepaths used Stuff's morphagenic abilities combined with a DNA sample of Cassandra Nova to create a synthetic copy of Nova's body. After Nova had been rendered fleshless, she sought refuge in the copied body but, on entering, Nova found herself trapped in a child-like state and forced to undertake pre-programmed tutelage.