The Fantastic Four is a fictional American team of comic book superheroes in the Marvel Comics universe. First appearing in the historically groundbreaking The Fantastic Four #1 (Nov. 1961), which helped to usher a new naturalism in the medium, they were the first superhero team created by writer/editor Stan Lee and artist/co-plotter Jack Kirby.

There are four core friends and family members traditionally associated with the Fantastic Four, who gained superpowers and turned into mutates after exposure to cosmic rays during a scientific space mission. The team consists of Mr. Fantastic (Reed Richards), a scientific genius and leader of the group who can stretch his body into incredible lengths and shapes. The Invisible Woman (Susan "Sue" Storm), Reed's wife and the team's second-in-command; she can render herself invisible and project powerful force fields. The Human Torch (Johnny Storm), Sue's younger brother, who can surround himself with flames, generate them as well, and fly. The final member is the Thing (Ben Grimm), their grumpy but benevolent friend, who possesses superhuman strength and endurance. His skin is monstrous, craggy, orange, and looks as if made of scales or plates (often mistakenly referred to as "rocks"). He is known for his great courage and fighting skill in addition to his strength.

Since the original four's 1961 introduction, the Fantastic Four have been portrayed as a somewhat dysfunctional yet loving family. Breaking convention with other comic-book archetypes of the time, they would squabble and hold grudges both deep and petty, and eschew anonymity or secret identities in favor of celebrity status. In the first two issues, the groundbreaking team do not even adhere to the "superhero" convention of costumes. After this the team wear uniforms specially fabricated by Reed that accommodate their individual powers.

The Fantastic Four was the foundation of Marvel Comics' ascent from a small division of a privately held magazine company to a major entertainment conglomerate. The team holds a pivotal place in the history of American comic books. The FF (as they are commonly known) has remained more or less popular, and has been adapted into other media, including four animated television series, an aborted 1990s low-budget film, the major motion picture Fantastic Four (2005), and its sequel, Fantastic Four: Rise of the Silver Surfer (2007).