This old Fantastic Four villain reinvented himself in 2006 when he damn near conquered the universe, and inadvertently brought the all-new, all-different Guardians of the Galaxy (a.k.a. the version everyone currently knows and loves) together in the first place. He's big, he's powerful, he looks scary as hell, he totally deserves a badass name like "Annihilus."
The all-powerful Anti-Monitor (whose name only makes sense with a LOT of context) destroyed an almost infinite number of universes, forcing the entire DC comic book line to reboot itself in the 1980s. Bad guys don't get much badder than this.
In some stories Bizarro is a failed clone of Superman, in others he's from a "bizarro" planet in which everything is the opposite of Earth. Either way, he's just as powerful as the Man of Steel and dangerously deranged, making him one of Superman's most popular villains for many years.
Another one of Superman's most popular bad guys, Brainiac is an alien android (in some versions, just an alien) obsessed with collecting intelligence from the around the universe. Some storylines claim he is directly responsible for the destruction of Krypton, others depict him as a destructive force that eliminates whole planets after he's learned everything about them.
Cassandra Nova is Charles Xavier's twin sister (sort of), who escaped from the womb and became the mirror image of everything he stood for. Professor X tried to bring about a new age of peace between mankind and mutants. Cassandra Nova was responsible for a genocide that left 16 million mutants dead.
There aren't many popular Batman villains who haven't shown up in theaters yet, but Clayface is easily the most prominent. An actor who fell victim to a toxic substance that melted him into clay, but gave him the ability to shapeshift into different people and deadly objects, Clayface is one of Caped Crusader's most powerful foes.
Kang the Conqueror is a little bit complicated, but time travel will do that to you. Basically he's a descendant of Reed Richards from the future, who became a time-hopping despot, who also became a more wizened villain named Immortus later in life, but thanks to time travel they sometimes work together. He's an ambitious villain, but the possibilities are inherently endless.
A lot of Spider-Man villains have animal powers (so does Spider-Man, obviously), so a big game hunter was always a natural fit. Kraven the Hunter may seem like a gimmick villain but his obsessive need to prove his superiority to Spider-Man eventually led to one of the hero's best and darkest storylines, Kraven's Last Hunt.
Warner Bros.' obsession with Lex Luthor and General Zod has left a lot of Superman's best villains on the cutting room floor. Here's another one: Metallo, a criminal trapped inside a powerful metal body, whose ability to rebuild himself - and his kryptonite battery core - has made him one of the Man of Steel's most formidable foes.
He's a big head with little arms and legs, and he's "Designed Only for Killing." This is M.O.D.O.K., one of Captain America's strangest and most unforgettable villains, who uses his mental powers to lead an army of evil super scientists.
This hard-to-pronounce villain (here goes: 'Mix-YEZ-pit-lick") is an all-powerful prankster deity from Dimension X, who routinely pops into Superman's life to stir up mischief. But Mr. Mxyzptlk is more than a joke character, he's been the cause of major strife in the DC universe on multiple occasions and, in a classic story by Alan Moore, revealed himself to be one of Superman's most dangerous adversaries.
One of the most fearsome alien races in all of comics, the Technarh are "techno-organic," alive but made of machinery, with the ability to transform themselves and infect other races. They formed The Phalanx and helped conquer the universe with Ultron as their leader, and proved themselves one of the most visually interesting and formidable threats in the Marvel universe.
Sinestro technically appeared in the live-action Green Lantern movie, but only as a hero, not as a villain. Once the most celebrated hero of the Green Lantern Corps, he eventually was revealed to be a corrupt influence, and went on to form his own army of Yellow Lanterns, who used their powers to instill fear across the galaxy.
Another mighty alien race, The Skrulls are a species of shapeshifters who have repeatedly infiltrated the ranks of Marvel's heroes in an attempt to conquer our planet. In the epic crossover event Secret Invasion, they came shockingly close.
Nowadays the Thunderbolts are a group of supervillains employed by the government, not unlike the Suicide Squad. But when they first premiered they had one of the cleverest ideas in comic book history: they impersonated a new team of superheroes, and defeated their fair share of other supervillains, to earn the world's trust. Then, when the time was right, they revealed their secret identities and took over the planet! Lots of these villains deserve to be the bad guy in a superhero movie, but that's such a clever idea that the Thunderbolts probably deserve their own film.