Gaheris (Old French: "Gaheriet", "Gaheriés", "Guerrehes", etc.) is a Knight of the Round Table in the chivalric romance tradition of Arthurian legend. A nephew of King Arthur, Gaheris is the third son of Arthur's sister or half-sister Morgause and her husband Lot, King of Orkney and Lothian. He is the younger brother of Gawain and Agravain, the older brother of Gareth, and half-brother of Mordred. His figure may have been originally derived from that of a brother of Gawain in the early Welsh tradition and then later split into a separate character of another brother, today best known as Gareth. German poetry also described him as Gawain's cousin instead of brother.
Malory's "Le Morte d'Arthur" depicts Gaheris as little more than a supporting character to Gawain, with an odd exception of his murder of their mother. However, his role is greater in French prose cycles that were Malory's sources, including as an object of murderous sibling rivalry by his older brother Agravain in the Vulgate Cycle. Inevitably, both there and in Malory, Gaheris is killed alongside his other brother Gareth during Lancelot's rescue of Guinevere, the event that will lead to the fall of Arthur.
Origin.
Gaheris and his brother Gareth likely originated from the same character of the only brother ever named for Gwalchmai ap Gwyar, the figure from Welsh mythology traditionally identified with Gawain. This character, a prince named Gwalchafed ["Gwalhafed"] or Gwalhauet ["Gwalhavet"] (Old Welsh for "Hawk of Summer") ap Gwayr or mab Gwyar, mentioned in "Culhwch and Olwen", is a likely common source for both Gaheris and Gareth, if Gawain was indeed derived from Gwalchmai. A later French-influenced Welsh romance "Seint Greal" does in fact call Gwalchmei's brother Gaharyet.
Medieval literature.
The names of Gaheris and Gareth (as used by Thomas Malory) have various similar forms in Old French works and the adventures ascribed to the brothers may be thus interchangeable and indistinguishable, as some writers even had them confused within the same manuscripts of a given text. Due their many and highly confusing French spellings, the International Arthurian Society described Malory's versions as "entirely different characters from Gaheriet and Guerrehes" of his sources, even as Malory might have not necessarily altered them himself.
Early appearances in French and German poetry.
In continental literature, Gaheris' name is first found as Gaheriet ("Gaherïet") on the list of King Arthur's knights in the French poem "Erec and Enide", written in the late 12th century by Chrétien de Troyes. He again appears in Chrétien's later "Perceval, the Story of the Grail", which describes him as a son of King Lot and as one of Gawain's younger brothers.
In Wolfram von Eschenbach's German poem "Parzival", the figure of Gaheriet is represented by Gawain's cousin named Gaherjet ("Gaherjêt"). Der Pleier's "Meleranz" mentions Gaharet (also rendered "Kaheret" in his "Tandareis and Flordibel"), described as a son of Arthur's sister Anthonje and the unnamed King of Gritenland, as one of the cousins of Gawain ("Gawan"), along with the protagonist Meleranz. As Karjet ("Karyet"), he also appears in Ulrich von Zatzikhoven's "Lanzelet", helping Lancelot rescue Guinevere from the abduction by King Valerin.
French cyclical prose and foreign adaptations.
The vast "Lancelot-Grail" (Vulgate Cycle) prose cycle of the early 13th century is the first known work to feature Gaheris as a major character. In the Prose "Lancelot", Gaheris is described as valiant, agile, and handsome (even as "his right arm was longer than the left"), but reticent in speech and prone to excess when angered. As such, he "was the least well-spoken of all his peers." Nevertheless, it tells how the nobles of the kingdom of Orkney (Orcanie), which his father King Lot had ruled when he was alive, attempt to have the kingdom given to Gaheris, whom they thought better fitted to be their king than any of his brothers (Gaheris, however, refuses to be crowned until at least after the end of the quest of the Holy Grail). The Prose "Merlin", too, describes him as the best warrior among Gawain's brothers, as well as at least equal to Gawain himself. 
The teenage Gaheris, together with Gawain and Agravain, defects from Lot and aids Arthur in the early wars against the rebel kings as well as the Saxons (substituted by the Saracens in some English versions such as "Arthour and Merlin"), especially distinguishing himself in fighting against the latter. Following their early battlefield feats, all three of them are knighted at once by Arthur in the Vulgate Cycle. However, Gaheris is the first of the Orkney clan to be knighted in the later rewrite known as the Post-Vulgate Cycle. In the Post-Vulgate "Merlin", when Gaheris is given flowers sent by the Queen of the Fairy Isle, it is prophesied that he would surpass in goodness and valor all the Knights of the Round Table save for two (presumably Galahad and Lancelot) were it not for the death of his mother, which Gaheris is destined to cause through his sin. The young knight then sets out in the quest to save Gawain and Morholt, during which he is twice attacked by his envious brother Agravain but soundly defeats him on each occasion. He eventually rescues both Gawain and Morholt, later accompanying the latter to Ireland.
Through the prose cycles, Gaheris then fights in Arthur's further wars against various enemies. He also often participates in his elder brother Gawain's chivalric adventures, in addition to these of his own, such as his rescue of King Bagdemagus. Some of these episodes are retold in Malory's compilation "Le Morte d'Arthur", where Gaheris (also written as "Gaherys" or "Gaheryes") is at first a squire to Gawain, whose fiery temper he helps moderate during their adventures, prior to being knighted himself. Gaheris later marries the haughty damsel Lynette, a sister of his younger brother Gareth's wife Lyonors. The "Lancelot" and the "Mort Artu" ("Death of Arthur") sections of the "Lancelot-Grail" cycle differ in their characterisation of Gaheris in relation to Gawain. In the "Lancelot", their youngest full brother Gareth is Gawain's most cherished sibling. In the "Mort Artu", it is instead Gaheris, and his death anguishes Gawain profoundly.
In the Post-Vulgate tradition (including Malory's telling), Gaheris takes part in the revenge killing of King Pellinore, the slayer of King Lot. More notorious is his beheading of his own mother, Queen Morgause, after catching her "in flagrante delicto" with Lamorak, Pellinore's handsome son and one of the greatest knights of Arthur. Lamorak is allowed to escape but is later hunted down alone by Gaheris with three of the other Orkney brothers (except Gareth), who believe Lamorak was the one who killed their mother. They ambush and fight him together, the act that is deemed cowardly and a blot on their honour, until his young half-brother Mordred stabs him in the back. When Arthur discovers that Gaheris is Morgause's real murderer, he is banished from the high king's court. Gaheris is then about to be beheaded in revenge for their mother's death by Mordred and Agravain, but Gareth convinces Gawain to order them to stop. Following his exile, Gaheris reappears as a companion of Perceval on the Grail Quest, having been earlier rescued by Palamedes from captivity.
In the Prose "Tristan", Gaheris is a friend of the eponymous protagonist Tristan, supporting him against the evil King Mark and forcing Mark to rescind Tristan's own banishment from Cornwall. The narrative of "Tristan" has Gaheris as a far better knight than Gawain, who here is villainized. Its Belarusian version "Povest' o Tryshchane" features him as Arthur's own son (rather than a nephew) by the name Garnot. In Malory's telling, however, Gaheris hates Tristan for being favoured by Arthur and is his sworn enemy. When Gaheris and Agravain meet and attack Tristan, the Cornish knight calls them and Gawain "the greatest destroyers and murderers of good knights" in the realm before fighting them off.
His death during Lancelot's rescue of Queen Guinevere from being burned at the stake is related in the "Mort Artu", the final volume of the Vulgate and Post-Vulgate prose cycles. While Gawain and Gareth will have nothing to do with Agravain and Mordred's plot to entrap Lancelot and Guinevere (in the English verse translation Stanzaic "Morte Arthur", Gaheris too sides with them), Arthur asks all the brothers of Mordred to help guard the queen's execution. Gaheris and Gareth reluctantly agree, though Gawain refuses. When Lancelot rushes to save the woman whom he loves, he cuts down the two Orkney princes. As told in the Vulgate "Mort Artu", Gaheris manages to kill Meliadus the Black, but then his helmet is knocked off by Lancelot's half-brother Hector de Maris, after which his head is split by Lancelot himself. Their surviving brother Gawain's fury is terrible, and the resulting new blood feud leads to the destruction of Arthur's kingdom.
Different characters by this name.
In the Post-Vulgate version of the "Mort Artu", a knight from North Wales also named Gaheris takes the vacant Round Table seat that had belonged to Gaheris of Orkney after the death of the latter. That 'new' Gaheris ("Gaheres de Norgales") participates in the resulting civil war, fighting on Arthur and Gawain's side against Lancelot's followers. To further confusion, there is also Gaheris of Karaheu, another Knight of the Round Table. Both of them are entirely distinct from Gaheris the brother of Gawain.
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References.
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