Put him on a planet and the Incredible Hulk is pretty much the biggest and baddest guy around. That's been his schtick since the character was created by Stan Lee and Jack Kirby put him to the page in 1962's The Incredible Hulk #1, but the character has gone through quite a lot of changes over the years. In some incarnations, he's a mindless brute while in others, he's the smartest strong-man in the Marvel Universe. Whatever his stats, the Hulk has fought against a lot of characters in his 55+ years of publishing, animation and film. In all that time, he's torn apart plenty of robots, but if there's one thing we know about the Marvel Universe, it's that not all robots are created equally.
Robots have been a part of the Marvel Universe since before the publishing company was even called Marvel. The first superhero ever printed under Timely Comics' brand (which would eventually become Marvel) was the Human Torch, an android created in a lab (more on him later). Since then, the House of Ideas has churned out robots whose power makes people like the Hulk look weak. Granted, the Hulk is a hero and despite being taken out and destroyed a number of times in the books, he always gets back up eventually. That being said, if the conditions were right and these robots were at the peak of their game, it's likely that any of these are 25 Marvel robots that can destroy the Hulk.
25 DANGER
Fans of the X-Men know they get their training done in a complex room full of holographic projectors, robots and intense battle programming. That room is appropriately called the Danger Room and it found a way to become sentient, which presented a rather dangerous problem.
Upon realizing she was the prisoner of the X-Men, the Danger Room lured a Sentinel to the school and used its parts to create a female robotic form to house her consciousness. She maintains a database full of every technique, trap and exercise the mutants have ever used making her a particularly dangerous robotic opponent for anyone, including the Hulk.
24 HULK-KILLER
Unsurprisingly, the Hulk-Killer was designed for the sole purpose of taking out the Hulk. It was created by the Leader and made to be even more powerful than its namesake/nemesis. It was recovered by General "Thunderbolt" Ross who had it activated by his scientists, but it ended up going on a rampage.
When the Hulk met up with it, the two fought. They pummeled one another for hours, but the Hulk-Killer gained the upper hand. The only way it was stopped was when Rick Jones intervened and was knocked down. Hulk reverted to Banner, which confused the Hulk-Killer leaving enough time to whip up a weapon capable of destroying the android.
23 DOOMSDAY MAN
After spending billions to send men to the Moon, the U.S. Government decided to move their cash towards automation and constructed a robot capable of exploring the vastness of space. The press dubbed the creation "Doomsday Man" believing it would one day be humanity's undoing... they weren't necessarily wrong.
Doomsday Man ended up escaping and wreaking havoc upon mankind. In terms of destructive power, Doomsday Man has an incredibly powerful laser cannon, a photonic nullifier, can "survive" in any environment including the vacuum of space, is of genius-level intellect and it can teleport. It could conceivable just pick up the Hulk and chuck him into the sun were it so inclined.
22 MACHINESMITH
When Samuel "Star" Saxon stumbled upon a discarded Doombot, his interest in robotics led him to take it apart and put it back together. What he learned enabled him to create robots of his own, which ultimately proved useful as he entered into a life of crime. He fought Daredevil multiple times, but succumbed to a fall and passed away.
His robots collected his remains and transferred his consciousness into a robot body. From then on, he was Machinesmith and possessed the ability to transfer his mind into more powerful robots. He is a criminal mastermind who is essentially immortal and able to possess the bodies of other robots making him a particularly dangerous foe.
21 RECORDER 451
There are powerful robots capable of ripping apart buildings and there are those whose intellect make them particularly dangerous. Recorder 451 is a Rigelian Recorder whose machinations on the planet Earth make him incredibly important to Marvel's continuity: he was responsible for the birth of Tony Stark.
451's interest in Stark isn't clear, but what is clear is that he used his knowledge and Kree technology to ensure the Starks' child would become Tony Stark, aka Iron Man. That foresight and ingenuity clearly establishes 451 as a significant member of Marvel's most important Robots. He couldn't beat up the Hulk, but he could probably set up some lethal traps long before that became an issue.
20 BLACK ANT
On the surface, a Life Model Decoy (LMD) isn't a huge threat in and of itself (not going to get into Aida here). Black Ant is such a device, but he is modeled after Eric O'Grady, the third Ant-Man who was destroyed by the Descendants. They sent Black Ant to join the Avengers in O'Grady's place where he successfully fooled the team for some time.
Eventually, his true identity was revealed and he was destroyed, but the Thinker rebuilt him. He is far more dangerous to the likes of the Hulk than other LMDs simply because he has the full use of Pym Particles, which have been used on/against the Hulk on multiple occasions.
19 THE FURY
In Marvel's wide multiverse there exists Earth-238, which was the home of The Fury, a robot designed for one purpose: take out every superhuman on the planet save for its inventor, Mad Jim Jaspers. When The Fury was unleashed upon its world, it succeeded in its mission save for one target, Captain UK who escaped to the Earth-616 reality of the standard Marvel Universe.
The Fury followed, but returned with the Jaspers of Earth-616 who failed to put up a fight and was destroyed. The Fury returned to Earth-616 once more where it remains an incredibly dangerous and powerful robot capable of destroying most superpowered beings who cross its path.
18 DOOMBOTS
Doombots are the creations of Dr. Doom for the express purpose of fooling his enemies and enabling him to essentially be in two places at once. They are programmed to fight or suffer through diplomatic negotiations in his stead. Each one has advanced AI and believe they are the true Doctor Doom.
A Doombot has many of the same powers as Doctor Doom, but on a slightly smaller scale. They are formidable and could pose a challenge to the Jade Giant. One Doombot... no, but hundreds or thousands of Doombots might just be able to give the Hulk a hard enough time to take him out.
17 ARSENAL
Back during the Cold War, Howard Stark whipped up a robot he called Arsenal who would go into service should the Reds win in the end. When that didn't happen, Arsenal, otherwise known as Project Tomorrow, was put into storage beneath the property that would eventually become Avengers Mansion.
Arsenal was activated when Titanium Man tried to contact Unicorn, which led it to believe it was imprisoned and the Avengers were all Commies it needed to destroy. Arsenal fought the Avengers and nearly won until Iron Man got involved. In the end, it was the Hulk who destroyed Arsenal, but things could have worked out differently leaving Arsenal the victor.
16 ULTIMO
Ultimo was the creation of a race of aliens who didn't like sharing the Universe with other people. It went out into the cosmos with the sole purpose of destroying anything and everything it came upon, which eventually led to its crash-landing on Earth where it was found by the Mandarin.
The Mandarin was able to repair Ultimo and reprogram it to become his henchman whom he used to defeat the Chinese Military. That brought Ultimo to Iron Man's attention and Ultimo was defeated. Unfortunately, Ultimo is easy to repair and it continues to return to service to wreak havoc on the Marvel Universe.
15 SUPER ADAPTOID
The Super Adaptoid was created with a shard of the Cosmic Cube, which rests within. It was designed for the sole purpose of destroying Captain America and has the ability to take on the appearance of Marvel's menagerie of superheroes, hence its name. It can also adapt multiple fighting styles and techniques to counter any threat.
When it wasn't able to defeat Captain America, it began creating new Adaptoids like itself to take on more targets, which brought it to the attention of the X-Men, the Avengers, and pretty much everyone else it wanted to fight and destroy.
14 SENTINELS
The Sentinels were created for the sole purpose of handling the "Mutant Problem" in America, but they have gotten out of hand more times than anyone can count. In the beginning, they were large, lumbering humanoid robots capable of capturing and imprisoning most Mutants, but they have evolved over the years.
The Sentinels depicted in X-Men: Days of Future Past were able to completely adapt their form, fighting style and even powers to take on every Mutant on the planet. If enough of them went up against the Hulk, there's no telling how long he could fight them before they got the upper hand.
13 LEOPARDON
Thanks to some hijinks back in the 1970s, Marvel made a deal with a Japanese production company to create a Spider-Man television show and the results were... interesting. Spider-Man was entirely different in several ways, but the biggest change to the classic character was the inclusion of a giant mechanized robot called Leopardon.
In the comics, Leopardon and Takuya Yamashiro hail from Earth-51778, but they made an appearance in Earth-616 during the Inheritor event. Leopardon is gigantic, has a massive sword, can withstand radiation and other forms of attack and packs a sonic knockout punch.
12 MEGATRON
Yes, you read that correctly: Megatron and the rest of the Transformers have been published over at Marvel for years even going so far as to cross paths with the likes of Spider-Man and many others. In terms of destructive power, it isn't clear how much damage his arm cannon could do to the Hulk, but that's hardly Megatron's most dangerous weapon.
Megatron is the leader of the Decepticons, which means he has an entire army of giant sentient robots under his command. His motto, "Peace through tyranny" and his sadistic goals mean he is more than a match for the likes of the Incredible Hulk!
11 OPTIMUS PRIME
Megatron isn't the only Transformer from Cybertron who found his way to Earth and the rest of the Marvel Universe. Every bad guy has someone who punches him in the face and for Megatron, that's Optimus Prime. Like Megatron, he has numerous weapons at his disposal and possesses a great deal of intelligence he could use to combat the Hulk, but he relies on something better to get the job done: his team.
Optimus Prime is the leader of the Autobots and like Megatron's Decepticons, his faithful army of gigantic sentient robots can bring the pain when the time comes.
10 NIMROD
The aforementioned Sentinels from Days of Future Past took a little something from a comic book counterpart named Nimrod. As an advanced model Sentinel, Nimrod differed from its peers in that it could modify its body to self-repair at the molecular level, reshape itself and alter its abilities to combat whatever threat it faces.
Nimrod eventually became sentient and could think for itself. It even went so far as to adapt a human identity called Nicholas Hunter. Whatever its guise, Nimrod is one of the most dangerous robots in the Marvel Universe and given the powers it can implement in combat, it is more than a match against the Hulk.
9 DEATH'S HEAD
Originally, Death's Head was introduced as a robotic bounty hunter in the UK Transformers title, but he didn't remain there for very long. Eventually, he found his way over to the standard Earth-616 reality where he became a nemesis of the Fantastic Four and the X-Men.
Death's Head has a lot going for him in the superpowers and "taking on the Hulk" department. As a Mechanoid, he can transform, he has strength that outclasses the Hulk, stands a good 30 feet high, is an expert martial artist and can shoot the wings off a flea from across the planet.
8 MASTER MOLD
The Sentinel Program was initially created by Bolivar Trask, a principal antagonist of Marvel's Mutants. As part of that program, Master Mold was created to perceive the threat of Mutants on earth and handle the "problem" by creating an army of Mark I Sentinels. This makes Master Mold the most dangerous of all the Sentinels due to its ability to continuously churn our an army of nearly unstoppable robots.
That's not all he has in his bag of tricks either. Master Mold possesses a genius-level artificial intelligence, can alter his size to epic proportions and can utilize the resources in its immediate area to reconstruct itself and its army.
7 HULK ROBOT
Originally, the Hulk Robot was little more than a mascot for a college all-star game, but the guy in charge of the project felt it was too dangerous to be used. It was a duplicate of the Incredible Hulk with all of his powers which made it pretty much unstoppable. It gained sentience from the Eternals and went on a rampage.
Hulk Robot was pretty much as powerful as the Hulk was when he wasn't too angry, but with the added sentience given to him by the Eternals, he stood a chance against the green guy. Ultimately, he was destroyed by the Red Hulk when he drained him of his radiation and tore him apart.
6 AIR-WALKER
Gabriel Lan was once a member of the Xandian Nova Corps, but found himself in the employ of Galactus as his herald. He was renamed Air-Walker, but is ultimately taken out by the Ovoids. Galactus revived his consciousness in robotic form, but found him lacking in the personality department so he was sent to find the Silver Surfer and recruit him back to Galactus' side.
Over the years, Air-Walker fought many galactic-level enemies to include Morg, Galactus' most ruthless and evil herald. In that battle, Air-Walker was completely destroyed, but had he taken the Power Cosmic to a fight against the Hulk, it's likely he would have come out on top.