1. Gareth is the youngest son of King Lot and Queen Morgause, King Arthur's half-sister, thus making him Arthur's nephew, as well as brother to Gawain, Agravain and Gaheris, and either a brother or half-brother of Mordred.

1. Gareth is the youngest son of King Lot and Queen Morgause, King Arthur's half-sister, thus making him Arthur's nephew, as well as brother to Gawain, Agravain and Gaheris, and either a brother or half-brother of Mordred.
Gareth is particularly notable in Le Morte d'Arthur, where one of its eight books is named after and largely dedicated to him, and in which he is known by his nickname Beaumains.
The earliest role of Gareth, appearing as Guerrehet, is found in the First Continuation of Chretien de Troyes's Perceval ou le Conte du Graal.
Gareth is set to work by Sir Kay, who always gives him difficult work, teases him as a lowly kitchen boy, and mockingly nicknames him "Beaumains" or "Good Hands".
Gareth receives much better attention from Sir Lancelot, who gives him gifts of clothes and gold for spending money.
Gareth goes to the aid of an unknown woman, later revealed to be the Dame Lynette, to save her sister Lyonesse from the Red Knight of the Red Lands.
Gareth is accompanied by the dwarf Melot, who knows his true identity.
Gareth then meets Sir Pertolope, the Green Knight, who mistakes him for his brother, the Black Knight.
Gareth overcomes the Green Knight but spares his life in return for the knight's swearing to serve King Arthur.
Gareth arrives at Lyonesse's castle, where she is besieged by Sir Ironside, the Red Knight of the Red Lands.
Lustily in love with Lyonesse, Gareth conspires to consummate their relationship before marrying.
Gareth was knighted by Lancelot himself when he took upon him the adventure on behalf of Lynette.
Later, Gareth tells Tristan he had parted ways with his brothers Gaheris and Agravain due to their dislike of him and their murderous ways.
In some other retellings, Gareth marries Lynette's sister, whom he rescues, and Gaheris marries Lynette.