What is the significance of the Ultimate Nullifier in Galactus's rivalries within Marvel comics?

The Ultimate Nullifier is a powerful cosmic artifact that represents the ultimate weapon, capable of erasing anything from existence. In his rivalry with Galactus, Reed Richards has leveraged the threat of using the Ultimate Nullifier against Galactus himself. This weapon has been instrumental in forcing Galactus to back down and spare worlds, as even the Devourer of Worlds fears its destructive potential, making it a crucial element in their confrontations.