"Ultimatum" is a 2009 comic book storyline published by Marvel Comics under its Ultimate Marvel imprint. It consists of a core five-issue eponymous miniseries written by Jeph Loeb and illustrated by David Finch that was published from January to September 2009, and a number of tie-in books. The storyline deals with Magneto's attempts to destroy the world following the apparent deaths of his children, Scarlet Witch and Quicksilver in The Ultimates 3.

Ultimate Marvel, later known as Ultimate Comics, was an imprint of comic books published by Marvel Comics, featuring reimagined and modernized versions of the company's superhero characters from the Ultimate Marvel Universe, later known as the Ultimate Universe. Those characters include Spider-Man, the X-Men, the Ultimates, the Fantastic Four, and others. The imprint was launched in 2000 with the publication of the series Ultimate Spider-Man and Ultimate X-Men in 2001, followed by The Ultimates and Ultimate Fantastic Four in 2002 and 2004 respectively providing new origin stories for the characters. The reality of Ultimate Marvel is designated as Earth-1610 as part of the Marvel Comics Multiverse.