Ultimate Nullifier
Ultimate Nullifier is a comic book object that first appeared in Fantastic Four Vol. 1 #50
The Ultimate Nullifier is a device that can eliminate from existence anything that the bearer chooses. It is powerful enough to destroy entire timelines if the bearer is of sufficient intellect and power.
The Ultimate Nullifier appears as a small hand-held silvery-metallic device with little or no apparent functionality, though it is possible that like Galactus, it appears differently depending on who is observing it.
The Ultimate Nullifier is capable of destroying any target the bearer directs the Nullifier at, if the bearer lacks the proper control, concentration, or power; the Nullifier will destroy the bearer as well and possibly the universe itself. While the origins of the Nullifier are largely unknown, it had been revealed that the Ultimate Nullifier is an aspect of Galactus himself. It is the only known object known to inspire fear in Galactus.
It was first given to Reed Richards by the Watcher when Galactus first appeared to devour earth. Reed threatened to use it against Galactus which Galactus became frightened so he left earth never to try to eat it again unless he was really hungry.
It later appeared during the Infinity War when Galactus had left Thanos and a number of Earth’s heroes aboard his starship as Galactus to plead his case on behalf of Adam Warlock to allow the Infinity Gems to function as one. As soon as he left the Magus appeared and kidnapped Warlock. Leaving Thanos with little in the way of options inquired about the Ultimate Nullifier’s location of Susan Storm. Nervously she betrayed it’s location with a look. Thanos picked it up and mentioned powerful and dangerous the weapon was, adding that it would require a far nobiler soul than his own to fire it. He then hand-picked Quasar out of the group of assembled heroes and asked: "How steely is your resolve, Quasar?", Quasar took the Nullifier and in an effort to learn as much as he could about consulted Epoch.
When Quasar arrived in the Magus’ dimension he was (unbeknownst to him) blanketed with an energy dampening field which disrupted the Nullifier, but not the Quantum-bands. When the controls of the dampening field were later damaged by Dr. Doom and Kang the Conqueror, Quasar was able to activate and slowly build power in the Nullifier, only to have it devastating effect turned against him by the Magus wielding an incomplete Infinity Gauntlet that was empowered by the Living Tribunal.
The Nullifier was next used when Morg took it from the hold in Galactus ship in an attempt to defeat Tyrant. The power of the Nullifier was temporarily contained by the Toady-Drone, which attached itself to Morg and fused them all together. Eventually the power was too great and it went off, destroying Galactus' ship and all on board.
Later, Abraxas, the embodiment of destruction attempted to destroy Galactus with the Nullifier, but Galactus demonstrated an ability to effortlessly call the Nullifier to his person.
In other media
In the video game Marvel: Ultimate Alliance, the Inhuman Medusa travels to Earth to find the Ultimate Nullifier and hopefully use it against Doctor Doom. This plan fails, as Doom expected someone would try and use it against her, and so uses his powers to brainwash Medusa.
In a side mission later on, players have to find the Ultimate Nullifier (which has been damaged). If it is found, Mr. Fantastic will one day fix it, and use it to repel Mephisto. If it isn't, then the team of heroes will have to join together again to stop Mephisto, with the resulting battle causing a massive amount of damage.
