A device published in the comics of Marvel Comics
. The Ultimate Nullifier first appeared in Fantastic Four #50
In the midst of the Cold War and the arms race between the United States and the Soviet Union, the people of the world had learned a valuable lesson greater and more powerful weapons and their inherent danger. So when Stan Lee and Jack Kirby introduced the ultimate nullifer in the mid-60's, the device was almost an allegory to the world scene.
The ultimate nullifier was a device small enough to be held in the hand of a normal adult male, but the small size belied its amazing power. Shaped like a half-moon, with a trigger on it, the ultimate nullifier had the ability to completely wipe from existence the target that the wielder intended. But as is the way of devices such as this, the power came with a price - the wielder too was wiped from existence.
The device first appeared when the world-eater Galactus first appeared on Earth. Intent upon consuming the biosphere of the planet and rendering it lifeless, Galactus was opposed by the Fantastic Four and his former herald the Silver Surfer. Those opposing Galactus were aided by one of the race known as the Watchers. Uatu, the member of this race that watches the events of Earth, sent one of the members of the Fantastic Four, the Human Torch, to Galactus's giant world-ship Taa II. There the Torch located and returned with the Ultimate Nullifier. Mr. Fantastic used the device to force Galactus to leave the Earth and promise never to return there. Galactus did so, though he trapped his former herald there for many years in punishment.
The Ultimate Nullifier has appeared a number of times over the years in various Marvel Comics. It was used by the hero Quasar against the villain Magus in the Infinity War and was used by Galactus's herald Morg against the entity known as the Tyrant as well, seemingly destroying the Tyrant, Morg, and Galactus himself, though Galactus was later shown to have survived.
After the death of Galactus, the evil entity known as Abraxas attacked all life in the universe. Abraxas was able to recover the ulitmate nullifier and intended to use it against all life. Through the efforts of Frankilin Richards, Galactus was returned to life and was able to wrest the weapon from Abraxas' grasp. Reed Richards used the device to expunge Abraxas from reality, but in the process destroying himself. Because of the way that the device works, the retroactive destruction of Abraxas rewrote the timeline of reality in such a way that Richards continued to exist even after his destruction.
The ultimate nullifier was also one of the 12 items of power that the Avengers and the Justice League of America battled over in the JLA/Avengers crossover.