The youngest true-born son of King Lot of Orkney and Morgawse, and brother of Gawaine, Gaheris and Agravaine.

Gareth was one of the best knights of his arms of the world and probably remains today the best loved of the Orkney brothers, as well as one of the best loved members of Arthur's Round Table. His story is quite familiar. The last of the brothers [except, presumably, Mordred] to come to court, he appeared anonymously and asked Arthur for three gifts.

The first was to be fed for a twelvemonth, at the end of which time he would ask another two. Kay took charge of feeding him, nicknamed him Beaumains ["Fair-hands"] in mockery, and put him in the kitchen. Both Lancelot and Gawaine befriended him, the latter not recognizing him as brother, and even Kay seems to have taken pride in Beaumains' strength in the sports of casting bars or stones.

At the end of the year, Lynette came to court requesting a champion for her sister Lyonors against Sir Ironside, alias "The Red Knight of the Red Launds", who was besieging their castle. Beaumains made his remaining requests: that he be given Lynette's adventure, and that Lancelot be sent after them to dub him knight on command.

To Lynette's chagrin, Arthur granted both gifts. Kay rode after them to give the kitchen boy his first test, and Beaumains promptly jousted him down; Lancelot came shortly thereafter and gave Beaumains a fall, but when they fought with swords, Gareth fought so well that Lancelot "dreaded himself to be shamed" and called a truce and knighted the young man.

Despite Lynette's continued mockery, Gareth completed the adventure, conquering and either converting or slaying numerous knights on the way - Gherard and Arnold le Breusse, the four brothers Percard, Pertelope, Perimones, and Persant, and finally Ironside himself. [Tennyson, who changes and simplifies the tale somewhat in one of his best idylls, Gareth and Lynette, ends it with Gareth's victory at Lyonors' castle and marries Gareth to the livelier sister, Lynette.]

Malory continues the story quite a bit further: Gareth begs to see the lady he has just saved from Ironside, but Lyonors tells him he must first labor for a year to win greater fame and her love. Already in love with him, however, she enlists her brother Sir Gringamore to bring him to her with a mock kidnaping of Gareth's dwarf. Biding together in the castle after this practical joke, Gareth and Lyonors decide to consummate their love in advance of the wedding ceremony, but Lynette uses a bit of magical art to keep her sister an honest woman.

Meanwhile, Pertelope, Perimones, Persant, and Ironside arrive at Arthur's court to describe their young conqueror's exploits. Queen Morgawse also comes to visit her brother Arthur, and her older sons learn of their relationship with Beaumains.

At Gareth's advice, Lyonors holds a great tournament at her castle on the feast of Assumption. Lyonors gives her lover a ring which enables him to fight in the tournament incognito, but he is recognized when his dwarf cunningly gets possession of the ring. Then Gareth slips away from the tournament and obtains lodging at the castle of the Duke de la Rowse by promising the Duchess to yield to the absent Duke whenever he meets him. Continuing, he kills a knight named Bendelaine in battle and defends himself successfully against twenty of Bendelaine's men who attack him seeking revenge.