The Marvel Universe is populated by powerful creatures, gods, Celestials, and personifications of abstract concepts, but even these almighty beings, from the Devourer of Worlds Thanos Wins."
Thanos is Marvel's ultimate villain. This is in part thanks to the unbridled success of the Marvel Cinematic Universe, where he was the "big bad" antagonist, but also because of his accomplishments in a long career in the comics. Starting with his experiments with the Cosmic Cube, Thanos showed the Universe that he is capable of acquiring and manipulating forces that go beyond a mortal's grasp. The most famous example is, of course, the Infinity Gauntlet saga, when Thanos became the supreme being in all reality and erased half the life in the universe with a snap of his fingers. During that classic story, Thanos faced all the supreme beings in the Marvel Universe and defeated them with no effort, a feat that he would repeat in the future. More than Thanos' obsession with Death, it's his fascination for absolute power that makes even the most powerful beings in the cosmos fear the Mad Titan.
"Thanos Wins" is a story arc beginning in Thanos #13, written by Donny Cates with art by Geoff Shaw and Antonio Fabela. In the story, Thanos is kidnapped by the Cosmic Ghost Rider and taken millions of years in the future to confront his future self, King Thanos, who has won all his battles and successfully conquered the universe. The plot then deals with Thanos' attempts to thwart this future to avoid becoming that version of himself, whom he deems a weakling. The most memorable part of the story is perhaps the very first page, where it is revealed that even the most powerful beings in the Marvel Universe harbor inside themselves one dark and hidden fear: one day even the greatest heroes will fail, and everything will die. This dreaded scenario will happen only in one case: if Thanos wins.
That first page serves as the setup for showing that dark future where Thanos actually wins but it also establishes the fact that the idea that Thanos will ultimately be successful in his nihilistic goals terrifies even the most powerful beings in creation. Over the course of his long and bloody career, Thanos has proved time and time again that he is capable of upsetting the balance of powers in the cosmos. He has obtained omnipotence several times, killed all the supreme beings in the universe more than once (including the One-Above-All, the supreme God of the Marvel Multiverse), and proved that, once he sets upon a path, his will is undeniable and inevitable.
While Eternals series, and ultimately all his attempts at omnipotence have been reversed (often by Thanos himself), the fact that he is this scary to every major force in the universe shows that Thanos has succeeded in becoming the boogeyman of all creation.
