The Marvel Universe is vast and full of terrors. Villains like Thanos and Galactus are constantly threatening life in the galaxy. But what would happen if the two were to threaten each other?
Which one of these cosmic titans are likely to come out on top in a battle? The fight itself would largely depend upon two factors: does Thanos have the Infinity Gauntlet, his signature brand of cosmic power-up... and just how well-fed does Galactus happen to be when facing down the Titan?
Regarding the first outcome, if Thanos doesn’t have the Infinity Gauntlet, the Mad Titan would be trounced. Galactus is a cosmic entity with power comparable to a god, he wields the power cosmic and must consume planets in order to survive. The Power Cosmic allows Galactus to transmute matter, create life, bring back the dead, and even destroy several solar systems at once (not to mention even give Thor himself a galactic upgrade). It’s clear that, despite being a powerful being in his own right, Thanos would be severely outmatched in this fight. This was even shown in Thanos: Epiphany #5, with the Mad Titan landing one hit on Galactus before being utterly beaten in return.
The outcome of this fight may change, however, if Thanos is given his most iconic piece of clothing - the Infinity Gauntlet. While Thanos should be able to defeat Galactus with all six Infinity Stones, he may also be able to defeat Galactus with one or two stones, depending upon Galactus' own power levels at the time. For instance, Thanos could use the Time Stone to figure out the best method of attack. If he only has the Power Stone, he could try to beat down Galactus through raw strength.
That being said, there is one final crux to any battle with Galactus that could turn a victory into a defeat. Galactus is considered to be a universal constant. He was created by Eternity at the beginning of the universe, and an embodiment of destruction lives within Galactus, preventing destruction from being outpaced by creation. If Galactus is killed, this destructive embodiment is released, and either leads to a cataclysmic explosion or the release of a villain known as Abraxas, an evil counterpart to Eternity and the destroyer of universes.
While Thanos could certainly beat Galactus if he had the Infinity Gauntlet, he may not even want to do so. Killing Galactus would leave the universe in a worse position, potentially even killing Thanos instantly in the process.