Antihero (sometimes spelled as anti-hero or two words anti hero) is a literary term that can be understood as standing in opposition to the traditional hero, i.e., one with high social status, well-liked by the general populace, and given a particular role to play. Although antiheroes may sometimes perform actions that most of the audience considers heroic, they continue because they must, not because they believe they are the right person for the job.

The "Racinian" antihero is defined by three factors. The first is that the antihero is doomed to fail before their adventure begins. The second constitutes the blame of that failure on everyone but themselves. Thirdly, they offer a critique of social morals and reality. To other scholars, an antihero is inherently a hero from a specific point of view, and a villain from another.

Typically, an antihero is the focal point of conflict in a story, whether as the protagonist or as the antagonistic force. This is due to the antihero's engagement in the conflict, typically of their own will, rather than a specific calling to serve the greater good. As such, the antihero focuses on their personal motives first and foremost, with everything else secondary.

An early antihero is Homer's Thersites, since he serves to voice criticism, showcasing an anti-establishment stance. The concept has also been identified in classical Greek drama, Roman satire, and Renaissance literature such as Don Quixote and the picaresque rogue.

An anti-hero that fits the more contemporary notion of the term is the lower-caste warrior Karna in the Mahabharata. Karna is the sixth brother of the Pandavas (symbolising good), born out of wedlock, and raised by a lower-caste charioteer. He is ridiculed by the Pandavas, but accepted as an excellent warrior by the antagonist Duryodhana, thus becoming a loyal friend to him, eventually fighting on the wrong side of the final just war. Karna serves as a critique of the then-society, the protagonists, as well as the idea of the war being worthwhile itself – even if Krishna later justifies it properly.

The term antihero was first used as early as 1714, emerging in works such as Rameau's Nephew in the 18th century, and is also used more broadly to cover Byronic heroes as well, created by the English poet Lord Byron.

Literary Romanticism in the 19th century helped popularize new forms of the antihero, such as the Gothic double. The antihero eventually became an established form of social criticism, a phenomenon often associated with the unnamed protagonist in Fyodor Dostoevsky's Notes from Underground. The antihero emerged as a foil to the traditional hero archetype, a process that Northrop Frye called the fictional "center of gravity". This movement indicated a literary change in heroic ethos from feudal aristocrat to urban democrat, as was the shift from epic to ironic narratives.

Huckleberry Finn (1884) has been called "the first antihero in the American nursery". Charlotte Mullen of Somerville and Ross's The Real Charlotte (1894) has been described as an anti-heroine.