The Wandering Jew (occasionally referred to as the Eternal Jew, a translation of the German "der Ewige Jude") is a mythical immortal man whose legend began to spread in Europe in the 13th century. In the original legend, a Jew who taunted Jesus on the way to the Crucifixion was then cursed to walk the Earth until the Second Coming. The exact nature of the wanderer's indiscretion varies in different versions of the tale, as do aspects of his character; sometimes he is said to be a shoemaker or other tradesman, while sometimes he is the doorman at the estate of Pontius Pilate.

An early extant manuscript containing the legend is the Flores Historiarum by Roger of Wendover, where it appears in the part for the year 1228, under the title Of the Jew Joseph who is still alive awaiting the last coming of Christ. The central figure is named Cartaphilus before being baptized later by Ananias as Joseph. The root of the name Cartaphilus can be divided into kartos and philos, which can be translated roughly as "dearly" and "loved", connecting the legend of the Wandering Jew to "the disciple whom Jesus loved".

At least from the 17th century, the name Ahasver has been given to the Wandering Jew, apparently adapted from Ahasuerus (Xerxes), the Persian king in the Book of Esther, who was not a Jew, and whose very name among medieval Jews was an exemplum of a fool. This name may have been chosen because the Book of Esther describes the Jews as a persecuted people, scattered across every province of Ahasuerus' vast empire, similar to the later Jewish diaspora in countries whose state and/or majority religions were forms of Christianity.

A variety of names have since been given to the Wandering Jew, including Matathias, Buttadeus and Isaac Laquedem, which is a name for him in France and the Low Countries in popular legend as well as in a novel by Dumas. The name Paul Marrane (an anglicized version of Giovanni Paolo Marana, the alleged author of Letters Writ by a Turkish Spy) was incorrectly attributed to the Wandering Jew by a 1911 Encyclopædia Britannica article, yet the mistake influenced popular culture. The name given to the Wandering Jew in the spy's Letters is Michob Ader.

The name Buttadeus (Botadeo in Italian; Boutedieu in French) most likely has its origin in a combination of the Vulgar Latin version of batuere ("to beat or strike") with the word for God, deus. Sometimes this name is misinterpreted as Votadeo, meaning "devoted to God", drawing similarities to the etymology of the name Cartaphilus.

Where German or Russian is spoken, the emphasis has been on the perpetual character of his punishment, and thus he is known there as Ewiger Jude and vechny zhid (вечный жид), the "Eternal Jew". In French and other Romance languages, the usage has been to refer to the wanderings, as in le Juif errant (French), judío errante (Spanish) or l'ebreo errante (Italian), and this has been followed in English from the Middle Ages as the Wandering Jew. In Finnish, he is known as Jerusalemin suutari ("Shoemaker of Jerusalem"), implying he was a cobbler by his trade. In Hungarian, he is known as the bolyongó zsidó ("Wandering Jew" but with a connotation of aimlessness).

The origins of the legend are uncertain; perhaps one element is the story in Genesis of Cain, who is issued with a similar punishment—to wander the Earth, scavenging and never reaping, although without the related punishment of endlessness. According to Jehoshua Gilboa, many commentators have pointed to Hosea 9:17 as a statement of the notion of the "eternal/wandering Jew". The legend stems from Jesus' words given in Matthew 16:28:

Ἀμὴν λέγω ὑμῖν, εἰσίν τινες ὧδε ἑστῶτες, οἵτινες οὐ μὴ γεύσωνται θανάτου, ἕως ἂν ἴδωσιν τὸν υἱὸν τοῦ ἀνθρώπου ἐρχόμενον ἐν τῇ βασιλείᾳ αὐτοῦ.