The third son of King Lot and brother to Agravaine, Gareth and Gawaine. Half-brother of Mordred and nephew to Arthur.

As Gaheriet, he appears among Arthur's knights in the list Chrétien de Troyes begins in line 1691 of Erec and Enide. Presumably this is the same Gaheriet whom Chrétien has Gawaine name as King Lot's third son in about line 8141 of Perceval. [Cline uses the spellings Gaheris and Gareth for Lot's third and fourth sons in this passage; D.D.R. Owen uses the versions Gaheriet and Guerrehet; "Guerrehet" seems not nearly so close to "Gareth" as to "Guerrehes", the name I found in the Vulgate for Gaheris. At this point, I can offer no clear explanation for these spellings.]

Vulgate IV remarks that Lot's third son was a good knight, and that his right arm was longer than his left.

He first came to court in youth with his mother and brothers Gawaine, Agravaine, and Gareth [who must have been very young indeed] when Morgawse visited Arthur between the two early waves of rebellion. Morgawse and her sons returned to Arthur's court after the second rebellion, at the burial af Lot; Morgawse clearly returned home afterward with Gareth, but the three older boys apparently stayed.

Before his own dubbing, Gaheris served as squire to his oldest brother Gawaine, toward whom he acted, at the same time, as a sort of advisor and second conscience. During the celebration of Arthur's marriage, when Gawaine said he would kill Pellinore in revenge for King Lot's death, Gaheris held him back, "for at this time I am but squire, and when I am made knight I will be avenged on him", and besides, if they killed Pellinore now they would trouble the feast. Pellinore's eventual death is not described in detail, but his widow complains that Gawaine and Gaheris "slew him not manly but by treason".

When Gawaine was sent on the quest of the White Hart, Gaheris, still his squire, accompanied him. On this adventure Gawaine defeated sir Ablamar and was about to ignore his plea for mercy when Ablamar's lady came between them and took Gawaine's stroke. As she fell headless, Gaheris rebuked his older brother:

Alas, said Gaheris, that is foully and shamefully done, that shame shall never from you, also ye should give mercy unto them that ask mercy, for a knight without mercy is without worship.

Retiring into Ablamar's castle for the night, Gaheris shrewdly warned Gawaine not to unarm: "Ye may think ye have many enemies here". Almost at once four knights angrily attacked Gawaine, and Gaheris fought very capably at his brother's side.

Like all his brothers, Gaheris became a knight of the Round Table. While Gareth was out on his first series of knightly adventures, Morgawse visited Arthur's court at Pentecost. Gawaine, Agravaine, and Gaheris, not having seen her for fifteen years, "saluted her upon their knees, and asked her blessing". Later, however, Gaheris slew his mother in anger at her taking Pellinore's son Lamorak for a lover. The two had an assignation at Gawaine's castle near Camelot, where Morgawse was staying on another visit, at her sons' invitation. Gaheris watched and waited as Lamorak went to the queen's bedroom.

So when the knight, Sir Gaheris, saw his time, he came to their bedside all armed, with his sword naked, and suddenly gat his mother by the hair and struck off her head. When Sir Lamorak saw the blood dash upon him all hos, the which he loved passing well ... [he] leapt out of the bed in his shirt as a knight dismayed, saying thus: ... Alas, why have ye slain your mother that bare you? with more right ye should have slain me ... The offence hast thou done, said Gaheris, notwithstanding a man is born to offer his service; but yet shouldst thou beware with whom thou meddlest, for thou hast put me and my brethren to a shame, and thy father slew our father; and thou to lie by our mother is too much shame for us to suffer. And as for thy father, King Pellinore, my brother Sir Gawaine and I slew him. Ye did him the more wrong, said Sir Lamorak, for my father slew not your father, it was Balin le Savage;

and as yet my father's death is not revenged. Leave those words, said Sir Gaheris, for an thou speak feloniusly I will slay thee. Bu because thou art naked I am ashamed to slay thee. But wit thou well, in what place I may get thee I shall slay thee; and now my mother is quit of thee; and withdraw thee and take thine armour, that thou were gone.

After Duke Galeholt's tournament in Surluse, Gaheris joined with his brothers (except Gareth) to ambush and kill Lamorak. As with other killings, Malory has his characters alude to the incident rather than describe it himself: finding that Gaheris and Agravaine have just killed a knight for saying that Lancelot was better than Gawaine. Trimstram rebukes the two brothers both for this and for Lamorak's death, of which he has just learned from Palomides. Tristram jousts them down and says he is leaving at that only for the sake of their relationship to Arthur. Remounting, they chase him in anger, and he unhorses them again.

Among other adventures, Gaheris fought the Cornish knight Matto le Breune and took away his lady, whose loss drove Matto out of his mind. Malory weds Gaheris to Lynette. Vulgate V gives him the Damoiselle de la Blanche Lande as a sweetheart. The accounts ar not mutually exclusive. Gaheris, like other knights, demonstrates considerable taste for sampling various damsels.

On at least one occasion Gaheris visited King Mark, bringing him and Isoud news of the Castle of Maidens tournament. Mark and Gaheris seem to have enjoyed each other's company well enough. Gaheris was among the guests at Guenevere's intimate dinner party when Sir Patrise was poisoned; Agravaine, Gaheris, and Mordred may have been present, however, largely because Gawaine and Gareth were invited. Gaheris took no part with Agravaine and Mordred when they trid to trap Guenevere with Lancelot. After Guenevere's trial, Arthur asked Gawaine to help lead the Queen to the stake. Gawaine refused.

Then said the king to Sir Gawaine: Suffer your brothers Sir Gaheris and Sir Gareth to be there. My lord, said Sir Gawaine, wit you well they will be loath ... but they are young and full unable to say you nay. Then spake Sir Gaheris, and the good knight Sir Gareth, unto Sir Arthur: Sir, ye may well command us to be there, but wit you well it shall be sore against our will; but an we be there by your strait commandment ye shall plainly hold us there excused: we will be there in peaceable wise, and bear none harness of war upon us.

According to the Vulgate, however, they were armed and fought back when Lancelot and his men attacked the guard to save the Queen. It is also hard to believe that Gawaine's statement of Gaheris' youth is to be taken literally. The result was the same in any case: Gaheris and Gareth were both killed.

To Gaheris further discredit, the Vulgate records how he widowed Lancelot's cousin "Iblis". Vulgate V, however, also depicts him showing a concern for common folk which other knights might also have shown, but examples of which are rarely recorded. While involved in settling a quarrel among the knightly class, Gaheris accidentally frightened a poor man. The poor man fled, leaving his donkey alone in the woods. Returning, he found it devoured by wolves. As the donkey had been essential to his livelihood, he would now be forced to beg. Gaheris, having inadvertently caused the trouble, requested his host - whose life he had just saved, and who thus owed him a favor - to give the poor man a horse. The host obliged, and the peasant's livelihood was saved.

In Sommer's edition of the Vulgate, the name Gaheries is given to the brother we know as Gareth, Malory's Gaheris being called Guerrehes in the Vulgate.