The amnesia of the protagonist, which he must struggle to penetrate, is a Plot Device common to most genres of popular literature. It has been used on innumerable occasions throughout the 20th century. In detective novels or thrillers – an example being Margery Allingham's Traitor's Purse (1941) – amnesia causes difficulties when the protagonist is accused of murder (or espionage) and must somehow penetrate the veil (or, in the case of hoax amnesia, pretend to) in order for the truth to be discovered; the trope is carried through to the cinema in the form of movies like The Morning After (1986). In sf, the amnesia of the protagonist will frequently conceal his true nature – superior mutation, android, robot, alien – or ultimate role: ruler of the sevagram, perhaps.
In fantasy, amnesia – which may be a medical condition, or sometimes nothing more diagnosable than an absence of knowledge – is generally a form of Bondage which conceals from the protagonist her or his true role in the Story whose unfolding may well unveil an ancient reality, revealing that he is the Avatar of an Elder God, or the god himself, or a Hero, or a Hidden Monarch, or a Changeling or a Fairy; or that he embodies the soul of a Malign Sleeper who now awakens (> Shadow); or that he is the Reincarnation of an ancient Magus or other figure of power or knowledge (or, when the amnesiac is female, of She). Amnesia may have been imposed upon the protagonist as a protection or as a Curse. It may be lifted through introspective study (this is not common), or through Initiation, or through the re-enactment of events anciently significant, or through tracing a Labyrinth, or through passing a Threshold, or through the action of Magic, often made effective by reading a Rune or by touching an Amulet or some other Talisman.
A typical amnesiac is the mortal soldier in A E van Vogt's The Book of Ptath (1947), who gradually discovers that he is the eponymous father of the gods. It is central to the Spell imprisoning Chessie, the enchanted purple Labrador in Nancy Kress's The Prince of Morning Bells (1981), that he not remember his name or life as a man. In Tim Powers's The Drawing of the Dark (1979), Brian Duffy cannot remember that he is in truth Arthur. As a punishment for having committed some sin he cannot now remember against a goddess whose name he does not know, the protagonist of Gene Wolfe's Latro sequence cannot remember anything for more than 24 hours: he writes his own story in short sequences, as an aide memoire. More typical examples (out of many) are the hero of Garfield and Judith Reeves-Stevens's Chronicles of Galen Sword sequence (1990- ), a human on Earth haunted by flashes of memory of his high status in an Alternate Reality; and the heroic warrior in Lisa Goldstein's Summer King, Winter Fool (1994) who, on being asked how he has escaped the sorcery-imposed bondage of amnesia, says simply, "I remembered who I was." The affliction is extremely common.
Fantasy amnesia – unless it is imposed at the end of a tale in order to protect the protagonist, or the world, or the god – exists in order to be removed. Amnesia, in other words, is almost invariably a form of suspense. [JC]