Gaheris ( ) is a Knight of the Round Table and a relative of King Arthur in Thomas Malory's Arthurian legend compilation Le Morte d'Arthur. He is the third son of one of Arthur's half-sisters, Queen Morgause, and her husband King Lot of Orkney. Gaheris is a younger brother of Gawain and Agravain, an elder brother of Gareth, and a half-brother of Mordred.
Malory's characters of Gaheris and Gareth both originate from the figure of Gawain's sole brother from the early Welsh Arthurian tradition. In the later French chivalric romances and their adaptations, this character was variably divided into two separate but often more or less interchangeable brothers, known as Gaheriet and Guerrehet among many other forms spellings, and the differences between them have been highly inconsistent prior to Malory's creation of a distinctive younger Gareth.
In Le Morte d'Arthur, Gaheris is portrayed largely as a supporting character to Arthur's chief nephew, Gawain, with the notable exception of his killing of their mother after finding her in bed with Lamorak. Ultimately, like their prototypes in Malory's French sources, Gaheris and Gareth are both slain during Lancelot's rescue of Guinevere, resulting in the downfall of Arthur's realm.
In German medieval poetry, where no equivalent of Gareth exists, a corresponding sole character appears as Gawain's cousin rather than his brother. In modern stories, Gaheris is often overshadowed by his brother Gareth but does appear in some major roles.
Origin
thumb|Galvagin (presumed [[Gawain|Gwalchmai/Gawain) being followed by Galvariun (possibly Gwalchafed/Gaheriet) on the Italian Modena Archivolt (c. 1120–1240)|left]]
Gaheris and his brother Gareth are thought to have originated from a single figure — the only brother traditionally named for Gwalchmai ap Gwyar, the figure from Welsh mythology generally identified with Gawain. This character, a prince named Gwalchafed (Gwalhafed) or Gwalhauet (Gwalhavet) — Old Welsh for "Hawk of Summer" — ap Gwayr or mab Gwyar, is mentioned in Culhwch and Olwen. He is a likely prototype for Gawain's brother Gaheriet His name could also inspire that of Galahad.
Medieval literature
The names of Gaheris and Gareth, as standardised by Thomas Malory in his compilation Le Morte d'Arthur, are used here for the purpose of simplicity and clarity. However, in Malory's sources — the various Old French prose romances — the two are found under a range of similar variants (such as a duo of "Guerrehés and Gaheriés"). Their adventures and character traits are often interchangeable or indistinguishable, and in some manuscripts the two are even conflated within the same text. According to R. H. Wilson, however,