"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.

Joseph "Jeph" Loeb III is an American film and television writer, producer and comic book writer. Loeb was a producer/writer on the TV series Smallville and Lost, writer for the films Commando and Teen Wolf, and a writer and co-executive producer on the NBC TV show Heroes from its premiere in 2006 to November 2008. From 2010 to 2019, Loeb was the Head of and Executive Vice President of Marvel Television.