A character (sometimes known as a fictional character) is a person or other being in a narrative (such as a novel, play, television series, film, or video game). The character may be entirely fictional or based on a real-life person, in which case the distinction of a "fictional" versus "real" character may be made. Derived from the ancient Greek word χαρακτήρ, the English word dates from the Restoration, although it became widely used after its appearance in Tom Jones in 1749. From this, the sense of "a part played by an actor" developed. Character, particularly when enacted by an actor in the theatre or cinema, involves "the illusion of being a human person." In literature, characters guide readers through their stories, helping them to understand plots and ponder themes. Since the end of the 18th century, the phrase "in character" has been used to describe an effective impersonation by an actor. Since the 19th century, the art of creating characters, as practiced by actors or writers, has been called characterisation.
A character who stands as a representative of a particular class or group of people is known as a type. Types include both stock characters and those that are more fully individualised. The characters in Henrik Ibsen's Hedda Gabler (1891) and August Strindberg's Miss Julie (1888), for example, are representative of specific positions in the social relations of class and gender, such that the conflicts between the characters reveal ideological conflicts.
The study of a character requires an analysis of its relations with all of the other characters in the work. The individual status of a character is defined through the network of oppositions (proairetic, pragmatic, linguistic, proxemic) that it forms with the other characters. The relation between characters and the action of the story shifts historically, often miming shifts in society and its ideas about human individuality, self-determination, and the social order.
This section needs expansion. You can help by adding to it. (January 2018)
In fiction writing, authors create dynamic characters by many methods. Sometimes characters are conjured up from imagination; in other instances, they are created by amplifying the character trait of a real person into a new fictional creation, or are created from scratch as a matter of expediency.
In his book Aspects of the Novel, E. M. Forster defined two basic types of characters, their qualities, functions, and importance for the development of the novel: flat characters and round characters. Flat characters are two-dimensional, in that they are relatively uncomplicated. By contrast, round characters are complex figures with many different characteristics, that undergo development, sometimes sufficiently to surprise the reader.
Dynamic characters are the ones that change over the course of the story, while static characters remain the same throughout.
In television, a regular, main or ongoing character is a character who appears in all or a majority of episodes, or in a significant chain of episodes of the series. Regular characters may be both core and secondary ones.
A guest character is one which acts only in a few episodes or scenes. Unlike regular characters, the guest ones do not need to be carefully incorporated into the storyline with all its ramifications: they create a piece of drama and then disappear without consequences to the narrative structure, unlike core characters, for which any significant conflict must be traced during a considerable time, which is often seen as an unjustified waste of resources.  There may also be a continuing or recurring guest character. Sometimes a guest character may gain popularity and turn into a regular one. 
In the earliest surviving work of dramatic theory, Poetics (c. 335 BCE), the Classical Greek philosopher Aristotle deduces that character (ethos) is one of six qualitative parts of Athenian tragedy and one of the three objects that it represents (1450a12). He understands character not to denote a fictional person, but the quality of the person acting in the story and reacting to its situations (1450a5). He defines character as "that which reveals decision, of whatever sort" (1450b8). It is possible, therefore, to have stories that do not contain "characters" in Aristotle's sense of the word, since character necessarily involves making the ethical dispositions of those performing the action clear. If, in speeches, the speaker "decides or avoids nothing at all", then those speeches "do not have character" (1450b9—11). Aristotle argues for the primacy of plot (mythos) over character (ethos). He writes:
But the most important of these is the structure of the incidents. For (i) tragedy is a representation not of human beings but of action and life. Happiness and unhappiness lie in action, and the end [of life] is a sort of action, not a quality; people are of a certain sort according to their characters, but happy or the opposite according to their actions. So [the actors] do not act in order to represent the characters, but they include the characters for the sake of their actions" (1450a15-23).
Aristotle suggests that works were distinguished in the first instance according to the nature of the person who created them: "the grander people represented fine actions, i.e. those of fine persons" by producing "hymns and praise-poems", while "ordinary people represented those of inferior ones" by "composing invectives" (1448b20—1449a5). On this basis, a distinction between the individuals represented in tragedy and in comedy arose: tragedy, along with epic poetry, is "a representation of serious people" (1449b9—10), while comedy is "a representation of people who are rather inferior" (1449a32—33).
In the Tractatus coislinianus (which may or may not be by Aristotle), Ancient Greek comedy is defined as involving three types of characters: the buffoon (bômolochus), the ironist (eirôn), and the imposter or boaster (alazôn). All three are central to Aristophanes' "old comedy".
By the time the Roman comic playwright Plautus wrote his plays two centuries later, the use of characters to define dramatic genres was well established. His Amphitryon begins with a prologue in which Mercury claims that since the play contains kings and gods, it cannot be a comedy and must be a tragicomedy.
[...] is first used in English to denote 'a personality in a novel or a play' in 1749 (The Shorter Oxford English Dictionary, s.v.).
Its use as 'the sum of the qualities which constitute an individual' is a mC17 development. The modern literary and theatrical sense of 'an individual created in a fictitious work' is not attested in OED until mC18: 'Whatever characters any... have for the jestsake personated... are now thrown off' (1749, Fielding, Tom Jones).