There are a lot of ways to answer this question, but ultimately it depends on who you ask and what criteria you use to determine strength. Here are a few of the most popular contenders for the title of strongest being in the universe:
The One Above All is a cosmic entity who is worshipped as a god by many Marvel characters. He is said to be the creator of everything in the Marvel Universe, and therefore he is incredibly powerful.
Thanos is perhaps the most well-known villain in the Marvel Universe, and for good reason – he’s incredibly powerful! Thanos has defeated some of the strongest heroes in the universe, including The Hulk and Thor.
Galactus is another cosmic entity who devours entire planets to sustain himself. He’s one of the oldest beings in existence and has taken on some of the mightiest heroes like The Silver Surfer and The Fantastic Four.
The Beyonder is an omnipotent being who created an entire universe just for fun. He once even transported all of Earth’s superheroes (and villains) to this alternate universe to see who would prevail in a fight. Needless to say, he’s pretty darn powerful!