Contains mild spoilers for Thor: Love and Thunder!
While Galactus is one of the biggest and baddest entities in all of Marvel Comics, even his world-devouring might is nothing compared to the MCU’s newest cosmic entity, Eternity, who just arrived in Thor: Love and Thunder. The cosmic entity's true nature means that no matter how powerful he grows, Galactus is literally incapable of competing with his 'father.'
The Devourer of Worlds made his first appearance in Fantastic Four #48, by Stan Lee and Jack Kirby. The gigantic entity is a survivor of the Sixth Incarnation of the Multiverse, empowered to consume energy in order to ensure the creation of the next incarnation of reality. He was reborn in the current Marvel Universe, awakening eons after the Big Bang with an unstoppable hunger for energy, which he can only draw from living worlds. This makes him one of the oldest and most powerful beings in the universe, and he has effortlessly defeated armadas of ships, the Avengers, and invading elder gods from outside reality. However, he is still only one part of the universe, and that is exactly why he falters against the cosmic entity Eternity.
Eternity first appeared in Strange Tales #138 by Stan Lee, Jack Kirby, and John Severin, as the anthropomorphic embodiment of the Marvel Universe. This literally means it is the sum total of all life in the universe. Eternity often manifests as a black robed entity with a half-hidden face and a body made of the very fabric of space and time, though it's able to manifest as any of the beings included in its totality - a list which includes Galactus. The Devourer of Worlds could never overpower Eternity because he himself is just a component part of its being, with Galactus' cosmic perspective even leading him to call Eternity 'father' on occasion. Galactus has grappled with other cosmic beings in the past, defeating some and being overpowered by others, but Eternity is above all of them because it is all of them combined, answering only to the Living Tribunal and One-Above-All, who exists outside any single reality.
However, Eternity and Galactus ultimately have no reason to seek each other’s destruction. Both entities are aware of each other and Eternity has even come to Galactus’ aid. During the Trial of Mr. Fantastic, Eternity was summoned by Galactus and the Watcher to allow millions of alien onlookers to become one with the universe. Through that connection Eternity helped them understand that Galactus is part of the natural order of life, often called the “Third Force of the Universe.” His purpose is to balance life and death, keeping the cosmic entities of Eternity and Death from each becoming more powerful than the other. In this way, Galactus generally exists to Eternity's benefit, and the two fighting would be like a person going to war with their own hand.
While MCU fans are still hoping to see Galactus on the big screen, even the Devourer of Worlds has limits - with one of the most fixed being his inability to rival a cosmic being formed of him, the Avengers, and every alien, monster, and god in the Marvel Universe. When it comes to power, Eternity is the benchmark, and Galactus exists in a very distant second place.
