As one of the most beloved comic-book-turned-cartoon heroes of the 90s, it's a common phrase among anime fans to ask "but can he beat Goku?" Dragon Ball's iconic lead character is not only one of the most powerful anime characters ever but rivals the likes of Superman and Saitama in terms of being one of the most powerful fictional characters ever, though that doesn't mean he's completely invincible.
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Indeed, Goku has been beaten countless times, and it's usually actually a tradition to have him lose against an arc villain before training and getting powerful enough to defeat our villain once and for all. However, there are several antagonists in particular that are leagues above the rest in terms of power, and these five, in particular, are not only the most powerful foes that Goku has fought but also the ones that dealt with him the quickest.
Vegeta
While Goku put up a fight against Vegeta during the climax of the iconic Saiyan Saga, in the end, he was no match for the Vegeta Oozaru form who crushed Goku like a bug. However, while this was the final thing that put the battle in Vegeta's favor, Goku had already been struggling prior to that. In the beam struggle that occurred, Goku ended up losing and was left severely weakened to the point where he would have likely lost the fight regardless.
It's this sheer power that puts into perspective just how Goku still had to go and is an important moment for the character as one of his most significant losses. Sure, Vegeta was taken down by his friends as they cut off his tail, but Vegeta would stick around as they traveled to Namek and faced off against Frieza and the Ginyu Force. In terms of sheer power, Vegeta's power has only grown from there, and has become one of the few characters who can stand toe to toe with Goku.
Cell
With the notable distinction of actually killing Goku as opposed to beating him, Cell's defeat of Goku was as swift as his own inevitable loss against Goku's enraged son Gohan. Prior to this, Cell had created the Cell Games as a way to prove his strength as the most powerful being in the world and Goku took him up on the challenge wholesale.
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Gohan, however, would fight Cell for the majority of the battle, with Goku only stepping in when Cell attempted to blow himself up in a final act is opposition. Goku, using Instant Transmission, transported himself to King Kai's planet and sacrificed himself to save Gohan - and Cell would live on a little longer due to a single cell of him surviving the encounter. It's not the noblest win of any character, but Cell's tenacity and strength ended up getting the better of Goku in the end.
Hit
An assassin from another universe, specifically Universe 6, Hit has the ability to "time-skip" which makes him a deadly foe to fight against as it's difficult to predict his next movements. Hit first appeared when Universe 6 made their debut and challenged Universe 7 to a tournament of fighters, with Hit and Goku eventually facing off in the ring together.
While the fight is hard, Hit clearly has the advantage over Goku and manages to keep him at arm's length throughout the fight. The battle eventually ended with Goku essentially forfeiting the match, Hit would have likely won as seen later on after the Future Trunks Saga - Hit would dispatch Goku with ease, albeit as part of a training deal Goku planned with Hit himself.
Golden Frieza
When Frieza returned from the dead, he had but one mission - to defeat Goku once and for all. After all, harboring a grudge against the hero while being stuck in a Hell of your own making will do that to a person. Through some once-in-a-lifetime self-reflection, he realized that he wasn't strong enough as is to defeat him and needed to unlock the latent potential within himself.
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And thus, Golden Frieza, his true final form, was unlocked, and Golden Frieza is nothing short of a force to be reckoned with. Goku, in his Super Saiyan Blue form as well, ends up losing to him, and Vegeta, who had just unlocked God Ki and was able to transform into Super Saiyan Blue, had to take over and while Vegeta nearly beats him, Frieza pulls a last-minute trick from his sleeve and destroys the planet. While Goku is able to go back in time and defeat Frieza for Vegeta in a funny comedic bit, it's still a testament to how powerful Golden Frieza actually is.
Fused Zamasu
One of the more bizarre yet obscenely powerful foes that Goku has had to fight, Fused Zamasu is the combination of both Goku Black and Future Zamasu into one being. Both characters, who are both technically different versions of Zamasu from different points in the timeline, have a hatred of mortals and wish to rid the universe of all non-god-like beings. Their own arrogance is backed up, however - they are simply that powerful.
In fact, Goku has to fuse with Vegeta to form Vegito in order to defeat him and that still isn't enough as Fused Zamasu is able to tank most of their attacks and very nearly kills them when the fusion runs out. It takes Trunks' final attack, Sword of Hope, to finally take him down, and it's a last-ditch effort from the energy of all his allies to even attempt it. As one of Fused Zamasu's original beings was Goku Black, one could say that the character that finally took down Goku was Goku himself.
Beerus
It's interesting in retrospect that Beerus debuted over 17 years after Dragon Ball Z initially ended as he feels like such an iconic part of the series for many fans at this point. In Battle of Gods, Beerus' first appearance, and Akira Toriyama's first time writing a new Dragon Ball story for the silver screen, fans were shocked when Goku actually lost his match to the Egyptian cat-inspired God of Destruction.
But it makes storywise, as Beerus is simply the most powerful character in the entire series next to Whis, his mentor, and Beerus' ability to go toe to toe with Goku without even using a fraction of his full abilities changed the game for how power scaling in the Dragon Ball universe worked. And while Beerus has evolved into an ally of sorts for the group, one can only wonder how Goku would fare against him now with all the new abilities he has acquired during Dragon Ball Super.
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