Few things are quite as tantalizing to comic book writers as definitive statements. What we mean by this is that comic book writers love it whenever there is something that is termed "unbreakable" or "undefeatable" or "invulnerable." The reason they like these definitive statements is that they give them the ability to break the unbreakable object, defeat the undefeatable and find vulnerability in the invulnerable. Thus, when a character is introduced as the "unstoppable Juggernaut," you better believe that comic book writers are going to come up with ways to... well, stop him.
Now, right from his first story arc in X-Men #12-13, which opened with a whole issue of Professor X just freaking his students out about the imminent arrival of the Juggernaut, we have established that there is a relatively realistic way to defeat the Juggernaut, which is to use telepathy to shut his mind down. However, the Juggernaut has prepared for that and he has a special helmet that protects him from such attacks. Therefore, the key to most fights with the Juggernaut is to get that helmet off somehow. Note that we are not counting the many times he has been depowered, like when he was a member of the X-Men or the Thunderbolts. We're only talking peak ability Juggernaut here, as otherwise it is not shocking when he loses! So here are the 20 most shocking times that the unstoppable Juggernaut has been stopped (in order of how unexpected the defeats were).
24 INCREDIBLE HULK #602
Following World War Hulk, Bruce Banner seemed stuck in his human form. That was a problem when his son from the planet Sakaar showed up. Hulk knew his Sakaarian wife was pregnant, but he thought the baby was lost when she was killed. It turned out the baby lived and then rapidly aged into Skaar, son of Hulk.
Skaar hung out with Banner while he waited for Hulk to return, as it was the Hulk that he wanted revenge on, not Banner. In the meantime, Banner trained him and had him fight the Juggernaut. Skaar successfully punched the Juggernaut into outer space!
23 SECRET WARS II #7
In Secret Wars II #6, the Beyonder temporarily destroyed Death itself. Mephisto secretly stored the energy that Beyonder used to destroy Death and used it to power a machine that would destroy the Beyonder (and a third of the universe) once he came into contact with a group of supervillains that Mephisto had tricked into helping him.
However, Mephisto had also given Thing extra powers to make sure that he would keep Beyonder busy until the villains arrived. Thing decided to defend the Beyonder and defeated most of the villains. Mephisto took the Thing's extra power away, but he still managed to keep the Juggernaut from getting to the Beyonder. In the end, time ran out and Mephisto's machine exploded.
22 AMAZING SPIDER-MAN #627
The classic Amazing Spider-Man writer, Roger Stern, returned to the character to tell a new story almost 400 issues after his original classic Spider-Man/Juggernaut fight. This time around, Spider-Man and Juggernaut are teamed up together to fight against the latest Captain Universe.
As it turned out, the Uni-Power ended up in the body of a man whose life was ruined during the aforementioned Spider-Man/Juggernaut fight, so he wants to kill Juggernaut, and Spider-Man has to save Juggy's life. The story opens with Juggernaut out cold in the park from Captain Universe's cosmic abilities, which are more than a match for Juggernaut's magic powers.
21 UNCANNY X-MEN #194
Inspired by his work on the Captain Britain series, Chris Claremont was going to bring a number of Alan Moore characters into the pages of the X-Men in the mid-1980s. Then, however, Moore began to make waves about whether Marvel owned the rights to the characters that he created in the Marvel UK stories. So Claremont had to change his plans abruptly.
Instead of using the powerful cyborg known as The Fury, Claremont instead introduced a mutant-hunting robot from the future known as Nimrod. In Uncanny X-Men #194, the X-Men were shocked to see Nimrod easily defeat the Juggernaut. Rogue had to absorb the powers of all of the X-Men to save their old foe.
20 VENOM: THE MADNESS #2
During the 1990s, Venom was so popular that Marvel had to give him his own series. However, they refused to make it an ongoing. Instead, he just had miniseries after miniseries after miniseries. In Venom: The Madness, Venom merged with a toxic virus that turned him into even more of a monster!
During this series, he scrapped with the Juggernaut a few times and he surprisingly defeated the "unstoppable" Juggernaut probably way more than he should have been able to. He even told him to shut up as he smacked him across a room! It is possible that the toxic virus somehow increased Venom's strength, as otherwise the Juggernaut should be way outside his league.
19 WORLD WAR HULK: X-MEN #3
World War Hulk saw the Hulk return to Earth to gain revenge on the Illuminati, who he believed had not only exiled him to another planet (which they did) but had also sabotaged his ship so that it would later explode, killing his new wife (they didn't do that). The X-Men tried to keep Hulk from Professor X.
The Juggernaut had been de-powered at the time, but embraced the power of Cyttorak to stop the Hulk, even though it meant returning to being a villain. He took on the Hulk full strength... but the Hulk then just used his momentum to send him flying into a lake.
18 X-MEN #13
The very first fight between the X-Men and the Juggernaut was going so poorly that Professor X actually had to use his powers to contact the Human Torch. The Torch showed up and he helped turn the tide. He attacked the Juggernaut with such ferocity that the Juggernaut was temporarily stunned.
During that moment, the Angel swooped in and took the Juggernaut's helmet off of his head, leaving him vulnerable to Professor X's psychic attack. In the years after this, the Juggernaut would better secure his helmet so that he couldn't be defeated by someone simply flying up to him and yanking his helmet off.
17 EXCALIBUR #3
The Juggernaut was in custody in England following a recent defeat by the X-Men when he was freed. He did not have his helmet on him,which of course left him vulnerable to psychic attacks. Otherwise he was just as powerful as ever. So when the newly formed British superhero team, Excalibur, showed up to stop him, they were out of luck.
Captain Britain's strength was no match for the Juggernaut. However, luckily, Excalibur had Rachel Summers, the daughter of Jean Grey from an alternate timeline, on their team and she easily defeated the Juggernaut with her telepathic powers. It would have been interesting to see if they could have gotten his helmet off.
16 INCREDIBLE HULK #172
The Hulk had actually been captured by the group known as the Hulkbusters, but the Hulk's strength was going to allow him to break out of captivity very soon. They tried in desperation to send him to another dimension, but that just switched him with Juggernaut, who had been left in another dimension during an earlier story. They freaked out and brought the Hulk back but now he and Juggernaut teamed up!
Soon, though, they began to fight each other and the Hulk easily tore his helmet off. He was about to attack the Hulk again, but then the X-Men luckily showed up and Professor X used his powers to knock the helmet-less Juggernaut out.
15 UNCANNY X-MEN #218
The X-Men had gone through a roster change and new members Dazzler, Psylocke and Longshot suddenly had to prove themselves in battle with the Juggeranaut, alongside their one "veteran" teammate, Rogue.
They used Longshot's luck powers for him to throw enough knives into the Juggernaut's armor that it luckily came off when Rogue then pulled on it. The Juggernaut had a back-up mask, but Dazzler then used her powers to cut that mask off with her lasers and then Psylocke used her telepathic powers to knock the Juggernaut out. This is a pretty much textbook way to defeat the Juggernaut. This defeat is what led to him being in captivity in England for Excalibur #3.
12 UNLIMITED ACCESS #1
DC/Marvel crossovers have not been kind to Juggernaut. In DC vs. Marvel #1, he was knocked down by Superman. We didn't see what happened next, so we didn't count it as an actual defeat. However, in a follow-up series, Unlimited Access, some DC characters showed up on the Marvel Earth and vice versa.
The Apokolips villain Mantis arrived on Marvel Earth and Wonder Woman followed behind. She and Spider-Man teamed up to force Mantis and Juggernaut to collide into each other, leading to them knocking each other out. Even before then, though, she seemed to be easily handling the Juggernaut.
11 INCREDIBLE HULK #404
The Juggernaut actually knocked the Hulk out in this story where he was working for the Red Skull. Juggy was disguised as a regular human, so he caught the Hulk by surprise. The Red Skull then used Mentallo to force the Hulk to fight the Avengers alongside the Juggernaut. The Hulk's psyche, though, caused him to turn on the Juggernaut, as he rebelled against Mentallo's authority, since he saw him as his abusive father.
He beat up Juggernaut badly and tore his helmet off. Then the psychic dissonance from him breaking out of the control of Mentallo knocked out all of the Avengers and Juggernaut, as well!
10 X-MEN: THE WORST X-MAN EVER #4
Bailey Hoskins is known as "the worst X-Man ever" because his mutant power is such that if he ever uses it, he will die. He has the power to explode, but he can't re-assemble his atoms. He would just outright blow up and never recover. While working with a group of other young mutants, they ran afoul of the Juggernaut. The heroic Bailey threw himself on the Juggernaut to protect his teammates that he had a crush on.
He was about to be smashed into little pieces when one of his teammates used her shockingly powerful reality-altering powers to just send Juggernaut into a well in the center of the Earth.
9 THOR #429
Juggernaut and Thor had a fight a year or so before this battle, and that fight was a bit of a draw. Their fight was so brutal that the ground under the Juggernaut collapsed and he fell into a big hole in the ground.
In their rematch, Thor discovered a key to their fight. He realized that since the Juggernaut is powered by magic, he could use the unique powers of his hammer to form a force field around their battlefield that blocked the magic from reaching the Juggernaut. He then beat the disconnected Juggernaut badly for the next 60 seconds, which is how long he can be separated from his hammer.
8 INCREDIBLE HULK #457
Following the events of Onslaught, Bruce Banner and the Hulk were separated from each other and Banner was seemingly killed. The Hulk was in a strange mental state being without Banner and it left him vulnerable to manipulation. Apocalypse stepped in and turned the Hulk into one of his Horsemen, making him his new War.
The Apocalypse-enhanced Hulk took on the Juggernaut and beat him senseless, using a special weapon Apocalypse gave him to brutalize the Juggernaut. In fact, the Hulk was almost about to kill Juggernaut when he was distracted and ol' Juggy took the opportunity to escape with his head still attached.
6 AMAZING ADVENTURES #16
Beast's defeat of the Juggernaut in Amazing Adventures #16 was part of a clever Marvel/DC unofficial crossover where a few DC/Marvel titles all went to the Rutland, VT Halloween parade at the same time. However, the defeat was one of those things that just came out of nowhere.
As it turned out, it appeared as though the Juggernaut would lose his powers and automatically age if anyone could take his helmet off. The Beast managed to get the helmet off, but he did not know about the odd spell that had been cast on the Juggernaut. Normally, he would have been easily beaten by the helmet-less Juggernaut, had it not been for this deus ex machina spell.
5 MARVEL TEAM-UP #150
In the final issue of the original Marvel Team-Up, Spider-Man teams up with the X-Men to take on Juggernaut and Black Tom Cassidy, who had been gifted with half of the Juggernaut's powers as a birthday present from his best friend.
Eventually, the X-Men manage to cut Black Tom off from the power, but that still left the Juggernaut, who seemed in total command of the fight. That is, he was until Rogue touched him and absorbed enough of his powers that he had no choice but to retreat. Rogue would later repeat her tactic here in the aforementioned Uncanny X-Men #218.
3 SPIDER-WOMAN #38
One of the most offbeat defeats of the Juggernaut happened when Spider-Woman teamed up with Colossus, Storm and Angel to take on Juggernaut, Black Tom Cassidy and Black Tom's ward, Siryn.
They were on a giant ocean liner and Storm and Spider-Woman decided to combine their electric powers to use the masts of the liner to become lightning rods to attack the Juggernaut. Colossus lured Juggernaut in between the masts and then Angel swooped in to fly Colossus out of the way of Storm and Spider-Woman's attack. Their blasts initially didn't do much until they set off an explosion and destroyed the entire ship, temporarily defeating Juggernaut!
2 AMAZING SPIDER-MAN #230
One of the most famous underdog victories in Marvel history is when Juggernaut arrived in New York City to kidnap the mutant psychic known as Madame Web. Spider-Man knew she would die after being disconnected from her life support chair for too long, so he had to stop the Juggernaut.
For two issues, he threw everything he could at the Juggernaut, but it was to no avail. Finally, he just attached himself to the Juggernaut's back and covered up Juggy's eyes and absorbed his blows while the Juggernaut blindly walked right into a pile of wet cement being used to construct a new building!
1 UNCANNY X-MEN #322
The most shocking defeat of the Juggernaut would have to be right after Age of Apocalypse, when the X-Men books picked up after a short hiatus. The X-Men were called to an explosion in New York, and it appeared as though someone literally punched the Juggernaut across New York State, knocking the "unstoppable" mutant out!
All he could say when he woke up was to fearfully warn the X-Men that, "Onslaught is coming!" At the time, writer Scott Lobdell didn't even know who Onslaught was, just that he was powerful enough to do that to Juggernaut. Eventually, we learned that Onslaught was a being made out of psionic energy caused when Professor X's mental powers were "infected" with Magneto's mind.