When it comes to attitude and brawn, few entities in the Marvel universe can match the Hulk. More often than not, he's as big a threat to the people he protects as he is to his enemies, especially when he loses control. The fundamental problem that Hulk's allies have with him is that his strength and size are directly proportional to his anger, meaning the more uncontrollable he becomes, the stronger he is.
Despite his seemingly infinite power ceiling, there were still those who dared oppose the Hulk at his worst. Only a few of them can withstand the Hulk's fury, much less take him on one-on-one. Nevertheless, he's far from unmatched, as some of these iconic Hulk villains proved.
10 THE RED KING
The Red King was one of the biggest off-world threats the Hulk ever faced. He was the ruler of the planet of Sakaar (not to be confused with Thor Ragnarok's Sakaar) and also served as the main villain of the comic book arc. Like most monarchs, the Red King was annoyingly pompous and believed he was a god who couldn't bleed... until he met the Hulk.
Thankfully, the Hulk taught the Red King some humility-- by destroying him and taking his crown. Hence, the Hulk became the usurper of the planet Sakaar, where he found peace and solace for a while. This is the Hulk we're talking about, of course, meaning there can be no lasting peace for him.
Wolverine is as much an enemy to the Hulk as he is an ally. He certainly has the attitude to match the Hulk's, and what he lacks in strength, he compensates for with his adamantium skeleton, extreme regeneration, agility, and animal senses. As it turns out, his adamantium claws can actually pierce and cut the Hulk, making their fight quite even.
The two former Avengers have fought many times in the comic books and animated shows. In fact, Hulk vs. Wolverine is as popular as Hulk vs. Thor, if not more so. However, it seems Hulk has the edge against Wolverine since he also has regenerative powers. Their fights usually end in a stalemate or with Hulk winning.
Thor can defeat Hulk. End of discussion. Really, he can, and that seems to be true both in the comic books and in the MCU. Unlike the Hulk, whose strength has to ramp up accordingly based on his emotion, Thor has that strength from the get-go. That and Thor's centuries of experience fighting is usually enough to defeat the Hulk quick enough when he wants to.
In a prolonged fight? Well, Thor's odds lower drastically. The two usually have a great deal of mutual respect for each other, based on their strength in the Avengers, but they've thrown down several times. When Thor finally learns how to use lightning to his advantage, he has proven to be even more of a challenge against the Hulk. Hulkbuster armor aside, he's the primary line of defense for when the Hulk lashes out, provided he's actually present.
7 THUNDERBOLT ROSS/RED HULK
The human General Thaddeus "Thunderbolt" Ross is one of Hulk's oldest and long-standing enemies. That's saying something, since anyone weaker than Hulk is usually crushed into a paste. One of the few reasons why Ross is still alive is because his daughter, Betty, was Bruce Banner's girlfriend for a time. As a general, Ross also mobilized and sent countless military forces to their doom just to defeat the Hulk.
In his lust for vengeance and obsession with the Hulk, Ross even became a Hulk himself, namely the Red Hulk. With the help of some of the shadiest minds on Earth, Ross was transformed into the Red Hulk. Eventually, Hulk defeated him after he overheated and even Thor could have killed him.
6 THE MAESTRO
Technically, the Maestro is not Hulk's enemy-- he IS Hulk, albeit from a different, parallel timeline to the original's. Still, this proves what we already know: the Hulk can be his own worst enemy. The Maestro was able to combine Bruce Banner's intellect and the Hulk's violent tendencies, resulting in a tyrannical reign where he ruled post-apocalyptic Earth with an iron fist.
The Maestro's regime got so bad, those who opposed him brought past "Professor" Hulk to the future in order to ask him for help to defeat his older and more experienced self. Too bad the Maestro seemed too powerful for the regular Hulk to defeat, even after two commendable attempts. So, regular Hulk and the rebels just sent the Maestro back to the original Gamma bomb which created them both. This disintegrated the Maestro... but didn't kill him.
The hardest decisions require the strongest will, and one of the hardest decisions for Thanos is facing the Hulk. After all, not many beings can match Thanos when it comes to strength. Like Thor, Thanos would have to end the fight quickly in order to have the upper hand. Once the Hulk's rage ramps up, he'll be unstoppable, even for someone as seasoned as Thanos.
That's basically what happened in the very beginning of Avengers: Infinity War. Thanos quickly took out the Hulk and humiliated him in the process. Still, any fan of the Hulk will know that he's one of the few who can single-handedly defeat Thanos. Even Thanos admitted in the comic books that the Hulk is one of the few beings he avoids conflict with.
Juggernaut is an unstoppable force, while the Hulk is an immovable object. So, when the two clash, you can bet the immense shockwave they create would be enough for another Big Bang and possibly create alternate timelines in the Marvel universe. Hulk's strength? Irrelevant. Juggernaut does not tire and is immune to almost any physical damage.
He is powered by Cyttorak, an ancient old god who's about as powerful as a Celestial. Depending on how much power Cyttorak lends to Juggernaut, he can either defeat the Hulk pretty early or their fight would result in a stalemate. Sadly (or perhaps luckily), they don't get to fight much.
There are many violent and evil men who desire Hulk's power, and some of them obtained it. One of them was General Ross, while the other is a KGB agent named Emil Blonsky. The result of their bloodthirsty disposition combined with the Hulk's powers? Catastrophic. The Abomination is the result of Emil absorbing bigger doses of Gamma radiation than the Hulk.
This essentially made the Abomination a bigger, worse, and uglier Hulk. To top that off, he also retained his mind and his military combat skills. He is one of the few beings who nearly killed the Hulk in their first encounter. Thankfully, the Hulk still won against Abomination because of his infinitely scaling strength and rage.
2 THE LEADER
Fighting fire with fire is not exactly the brightest way to defeat your enemy. Samuel Sterns is Hulk's smartest enemy and has proven to be more dangerous than some of his strongest villains. As a janitor working at a lab, Samuel was accidentally bathed in Gamma waste after moving one of its containers. This caused him to mutate-- his head and brain became oversized; it even improved his intellect by a thousand-fold. He assumed a different name, The Leader, using intelligence to turn the world into his own giant chess board.
His plans were quite simple: to become a criminal mastermind and eventually take over the United States. By bad luck, he stumbled upon Bruce Banner and the Hulk in doing so, and he has since hated both of them. Lacking strength, of course, The Leader had to resort to diabolical low-blows against both the Hulk and Bruce Banner. In fact, one of the most spiteful things he did to Banner was ruining his wedding by turning him into the Hulk.
1 THE FORCES OF EARTH
Well, not exactly the whole Earth, but rather its biggest brains. Tony Stark (Iron Man), Reed Richards (Mr. Fantastic), Dr. Strange, and Black Bolt forcibly exiled the Hulk to his own "safe planet" where he wouldn't be able to hurt anyone-- but his spacecraft malfunctioned and he ended up on the hostile world of Sakaar.
Nothing hurts more than being betrayed by the very people you trust. So, in World War Hulk, the HulK, burning with thoughts of revenge he nursed while conquering Sakaar, unleashed retribution against the Earth for betraying him. With his Sakaar armada in tow, he nearly won against Earth, Avengers and all-- but was stopped short by Sentry after an exhaustive brawl that turned him back into Bruce Banner. Crisis averted.