"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.

In the Ultimate Marvel universe, Thorlief "Thor" Golmen is a fictional superhero based on the Marvel Universe version of Thor, who is the Asgardian God of Thunder and a founding member of the Ultimates. Also known as "Ultimate Thor", Golmen is an anarchist who discovers he is the reincarnated form of the Norse warrior god Thor. The "Ultimate" redesign of the character reduces the number of Thor's powers, and reduces the character's reliance upon his hammer. Perhaps most significantly, the Thunder God's long-established personality is drastically altered, changing him from an eager and willing divine combatant into an ecocentric, arguably unstable, and reluctant warrior.