A superhero or superheroine, is a character who typically possesses superpowers or abilities beyond those of ordinary people, is frequently costumed concealing their identity, and fits the role of the hero, typically using their powers to help the world become a better place, or dedicating themselves to protecting the public and fighting crime. Superhero fiction is the genre of fiction that is centered on such characters, especially, since the 1930s, in American comic books (and later in Hollywood films, film serials, television and video games), as well as in Japanese media (including kamishibai, tokusatsu, manga, anime and video games).

Superheroes come from a wide array of different backgrounds and origins. Most superheroes (for example, Superman and Spider-Man) usually possess non-human or superhuman biology, while others (such as Batman and Iron Man) derive their status from advanced technology they create and use, but some of them may use or possess objects that have superhuman, mystical, or alien powers (such as Green Lantern and He-Man), or study and practice magic to achieve their abilities (such as Doctor Fate and Doctor Strange). The Dictionary.com definition of "superhero" is "a figure, especially in a comic strip or cartoon, endowed with superhuman powers and usually portrayed as fighting evil or crime," and the Merriam-Webster dictionary gives the definition as "a fictional hero having extraordinary or superhuman powers; also: an exceptionally skillful or successful person." Terms such as masked crime fighters, costumed adventurers or masked vigilantes are sometimes used to refer to characters such as the Spirit, who may not be explicitly referred to as superheroes but nevertheless share similar traits.

Some superheroes use their powers to help fight daily crime while also combating threats against humanity from supervillains, who are their criminal counterparts. Often at least one of these supervillains will be the superhero's archenemy or nemesis. Some popular supervillains become recurring characters in their own right.

Antecedents of the archetype include mythological characters such as Hanuman, Gilgamesh, Odysseus, and David, and demigods like Heracles, and Perseus, all of whom were blessed with extraordinary abilities, which later inspired the superpowers that became a fundamental aspect of modern-day superheroes. The distinct clothing and costumes of individuals from English folklore, like Robin Hood and Spring-Heeled Jack, also became inspirations. The dark costume of the latter, complete with a domino mask and a cape, became influential for the myriad of masked rogues in penny dreadfuls and dime novels.

The vigilantes of the American Old West also became an influence to the superhero. Several vigilantes during this time period hid their identities using masks. In frontier communities where de jure law was not yet matured, people sometimes took the law into their own hands with makeshift masks made out of sacks. Vigilante mobs and gangs like the San Diego Vigilantes and the Bald Knobbers became infamous throughout that Old West era. Such masked vigilantism later inspired fictional masked crimefighters in American story-telling, beginning with the character Deadwood Dick in 1877.

The word superhero dates back to 1899. The 1903 British play The Scarlet Pimpernel and its spinoffs popularized the idea of a masked avenger and the superhero trope of a secret identity. Over the next few decades, masked and costumed pulp fiction characters such as Jimmie Dale/The Grey Seal (1914), Tarzan (1912), John Carter (1912), Zorro (1919), Buck Rogers (1928), The Shadow (1930), Lensman (1934) and Flash Gordon (1934), film serial heroes Judex (1916) and Ravengar (1916) and comic strip heroes such as the Mandrake the Magician (1934), Magic Phantom (1935), Phantom (1936), began appearing, as did non-costumed characters with super strength, including the comic-strip characters Patoruzú (1928) and Popeye (1929) and literary characters such as Hugo Danner (Gladiator, 1930) and Aarn Munro (The Mightiest Machine, 1934). Another early example was Sarutobi Sasuke, a Japanese superhero ninja from the Japanese folklore and children's novels in the 1910s; by 1914, he had a number of superhuman powers and abilities. France produced early examples like the superheroine L'Oiselle, ccreated in 1909 by French writer Renée Marie Gouraud d'Ablancourt under her pen name René d'Anjou. The character, whose real name is Vega de Ortega, is notable as one of literature's earliest winged heroines, utilizing artificial wings for flight and the cyborg Nyctalope (1911), possessing two revolutionary enhancements for the period - enhanced nocturnal vision and an electromechanical cardiac implant, Famany, the "flying man" of a German comic story of 1937, who uses a winged apparatus to fly over New York and who becomes embroiled in the world of crime, had only one appearance.

The pulp magazines of the 1930s served as a crucial breeding ground for early superhero concepts through their innovative comic features:

In August 1936, Thrilling Wonder Stories published Zarnak by ax Plaisted. In August 1937, a letter column of the magazine, the word superhero was used to define the title character. Another groundbreaking character emerged in August 1937, Olga Mesmer, "The Girl with the X-ray Eyes," featured in a single-page comic strip in Spicy Mystery Stories.