Sir Bors was the favourite cousin of Sir Lancelot, and the son of King Bors of Gannes (probably Vannes in Brittany) & Queen Evaine. After the death of King Bors at the hands of King Claudas, his young sons, Bors the Younger - who had nominally succeeded as King - and Lionel, were taken into captivity. They were, however, rescued by Seraide, High-Priestess of the Lady of the Lake, to whom she entrusted their care. They were thus brought up with their cousin Lancelot.

Bors travelled to King Arthur's court with Lancelot. Along with Gawain and Bedivere, he acted as a messenger between King Arthur and his Imperial Roman enemy, Lucius. Subsequently becoming a central figure in the King's European campaigns as Arthur's personal guard. He became a great warrior, wielding Duke Galeholt's sword and easily recognized by a distinctive scar on his forehead.

Sir Bors came to the attention of the daughter of King Brandegoris of Stranggore who desired to be the centre of his attentions. Although he was an avowed chaste Knight of the Round Table, she conspired with her nurse to have him pleasure her. With the aid of a magic ring, the lady's servant enchanted Bors into making love to the princess and, as a result, he became the father of Helain le Blank. Despite this indiscretion, Bors' purity enabled him to become an important Grail seeker.

During his quest, Bors stayed at the castle of King Amans and championed his younger daughter. He was living an austere life at the time, eating only bread and water and sleeping on the floor. During the night, he had two dreams showing him the choices he would face the following day. Should he save his brother, Lionel, from captivity and torture or a virgin from deflowerment? Should he make love to a temptress or allow her and her maidservant to jump from their tower? He chose the latter option in each case. Lionel was not happy at being abandoned by his brother and later attacked him in a blazing rage. Bors refused to defend himself, but a hermit was killed when he tried to intervene and Bors was forced to take up his weapon. A column of fire from Heaven finally stopped the fight. Along with Galahad, Percivale and Amide, Bors became the third of the Round Table Knights to achieve a viewing of the Holy Grail. He was the only one to return alive to Arthur's court.

Despite his innocence, Bors took it on himself to advise Lancelot concerning his affair with Queen Guinevere. He even acted as peacemaker for the adulterous pair and, later, accompanied Lancelot into exile, where he was given the lands of King Claudas. He returned, at Lancelot's side, during the Civil War with King Arthur and when extinguishing the remnants of Mordred's rebellion. Bors eventually joined Lancelot at his hermit retreat, but, after the latter's death, he returned to Gannes to put his house in order. Finally, he left, with Sirs Ector, Blamore and Bleoberis, to fight on Crusade in the Holy Land where he was killed.

In origin, Bors may have developed from the mythical Welsh character, Gwri alias Pryderi.