Ultimate Nightmare was the first part of the Ultimate Galactus Trilogy but was not originally planned to be so. In the original plan, Ultimate Nightmare, written by Warren Ellis, was intended to be more of a prologue to an Ultimate Universe-wide event written by Mark Millar. However, health issues motivated Millar to bow out of the project, leaving Ellis to handle the entire event. Joe Quesada had an idea to change its format, and Ultimate Nightmare instead became the first of a trilogy of limited series.