When you think of Fantastic Four villains, the first name that comes to mind is obviously Dr. Doom, one of the greatest villains in all of Marvel comics. He's a great main foil for the team to have, but he's far from the only heavy hitter that first family has to deal with nor is he the only interesting rogue in their gallery, contrary to what Fox movies would lead you to believe.
Their gallery spans from cosmic threats to the Negative Zone and everything in between, giving them such a variety of villains to go up against, all challenging them in their own way. This list won't be ranking them based on power, but rather in terms of how impactful they are from a story sense. To preface as well, Namor flip flops too often to make this list.
10 Red Ghost
At a glance, Red Ghost can seem like a fairly lame villain, an older Russian scientist who relies on highly intelligent apes to do his bidding. It isn't exactly eye-catching, but what makes him so intriguing, is he got his powers the very same way as the Fantastic Four. They both gained it from cosmic rays, making him the evil version of the four, even if their powers differ. His role within the Intellgencia was one of the better takes on the character, showing off just how intelligent he and his apes could be, paying him the respect he doesn't often get.
9 Puppet Master
While Puppet Master may not have the most exciting ability, controlling people via clay puppets, his hatred of The Thing earns him a spot on this list. The reason for that is he happens to be the father of Alicia Masters, Ben's leading romantic interest. This tie in gives him a link to the team, letting intensely personal tales be told. Many of his better stories revolve around the dynamic he has with his daughter rather than when he becomes a human trafficker or at one point, comes in possession of the power cosmic.
8 Ronan The Accuser
Fans of the MCU may only know Ronan from Guardians of the Galaxy as well as Captain Marvel. They both capture the character fairly well, aside from the hilarious dance battle scene at the end of Guardians. The only thing that could have been driven home a bit better is Ronan's zealotry, the man practically being a space templar.
Many of his better stories are firmly in the cosmic universe of Marvel, but his zealotry is a very nice contrast to Reed's more rational mind. His lower place on this list, mostly being due to him not being a primary villain for the Fantastic Four.
7 Mad Thinker
Mad Thinker is one of the few villains who actually comes within the same stratosphere as Reed in terms of intelligence. While he does get outsmarted plenty, he's shrewd enough to use misdirection, making the Four think they've outsmarted him when all they did was stop the pretext of his plan rather than his real goal. The slow break of his sanity has been pretty great, especially in regards to his obsession with Reed now. It's different than Doom's, wanting to be the new Reed rather than prove that he's the smarter of the pair.
6 Wizard
Wizard is one of the more underrated villains in the Fantastic Four's rogue gallery. His creation of the Frightful Four is a great idea, fighting as a team making more sense than trying to win a four on one with the Fantastic four. Who makes it in the group is often ever-changing though Wizard is often a constant catalyst. As with the Thinker above him, he's a genius, making it far more difficult for Reed to win battles through pure intelligence. It's why Wizard was among those in the Inteligencia, the smartest super-criminals in the Marvel universe.
5 Mole Man
If we are talking underrated villains, Mole Man should be at the top of the list. He should also be near the top of the villain list for the Fantastic Four's inevitable MCU film. While Namor is often the go-to villain when they want to do a nation rising up to try to take over the surface world, Mole Man is a superior villain.
The reason for that he can be painted in so many ways depending on the writer. He can be a bloodthirsty dictator who hates the surface world and wants to destroy it or you can make him incredibly sympathetic, his world being a haven for outcasts. At his best, he's closer to the latter.
4 Galactus
Galactus is such a unique villain in the pathos of Marvel, one that isn't your standard evildoer, more a force of nature. It's why many predict him to be the next big force the Marvel world will need to team up to deal with. He's an entity that is forced to devour planets to continue its existence. All of us are merely a food source for him, looking at us no more than we would a hamburger. He provides such a presence of impending doom, something so few villains can manage.
3 Annihilus
Another villain pitched for the Fantastic Four's MCU film has been Annihilus, a villain those not well versed won't be aware of. He's the ruler of the Negative Zone, an antimatter dimension found by Reed Richards. Given his stature and power, he's far better suited to be the bad guy in a follow-up movie. His power rivals that of any cosmic being not named Galactus, as shown in the amazing series "Annihilation". It's what makes him such a dangerous foe for Reed and the Fantastic Four.
2 Super Skrull
Some may feel he's too high on this list, but he has a genuine reason to hate the Fantastic Four that neither Annihilus or Galactus do. He feels as if they are the cause of the destruction of his homeworld, at the hands of Galactus no less. That thirst for revenge plus his dedication to the Skrull empire as a soldier makes him an incredible villain for the team to go up against. He can provide both a physical challenge as well as provide a compelling story (shown especially well in the cosmic universe).
1 Doctor Doom
Was there any doubt who would take the top spot here? There's a reason he's been the bad guy in every single Fantastic Four movie. He's the best they have, for more reasons than just being a former colleague of theirs. That emotional connection helps, but it's his personality that makes him so intriguing and memorable. No one else can find a way to ooze charisma and megalomania at the same time, quite like Doom can. The sheer fact he speaks the way he does is another plus.