Sir Pertolepe is the Green Knight encountered immediately after Sir Gareth defeats and kills Sir Percard, the Black Knight. He is one of four brothers associated with the series of perilous encounters that Gareth faces while travelling with Dame Lynette towards Castle Dangerous.

Gareth is still publicly known as Beaumains and is wearing Percard’s black armour and riding Percard’s horse. When Pertolepe sees the approaching black-armoured rider, he asks Lynette whether she has brought his brother back with her. Lynette tells him that the rider is not Percard but the kitchen knave who has killed him.

Pertolepe mourns Percard as a noble knight and angrily challenges Gareth. Gareth responds that Percard was killed honourably in combat rather than through treachery or shame. Pertolepe then rides to a green horn hanging from a thorn and blows three notes. Two damsels appear and arm him, after which he mounts a great horse and takes up a green shield and spear.

The two knights charge one another with such force that both spears break. They draw their swords and exchange heavy blows, wounding one another severely. During the mounted fighting, Gareth’s horse strikes Pertolepe’s horse in the side and knocks it to the ground. Pertolepe quickly rises, and Gareth dismounts so that they can continue the battle on equal terms.

They fight on foot for a long time. Pertolepe delivers a powerful blow that splits Gareth’s shield, but Gareth answers by striking him on the helmet and forcing him to his knees. Gareth then pulls the Green Knight to the ground and prepares to kill him.

Pertolepe asks for mercy and offers to forgive Gareth for Percard’s death. He also promises to become Gareth’s man and to place thirty knights under his command. Gareth refuses to spare him unless Lynette herself asks for his life. Although she has continued insulting Gareth throughout the journey, Lynette finally orders him not to kill the Green Knight.

Gareth accepts her request and releases Pertolepe. The Green Knight kneels and performs homage with his sword. His response to defeat distinguishes him from Percard: he accepts Gareth’s victory, abandons his demand for vengeance and immediately begins assisting the man who overcame him.

Pertolepe invites Gareth and Lynette to stay at his nearby manor. At supper he objects to Lynette’s continuing abuse of Beaumains, declaring that Gareth has proved himself a nobler and stronger knight than Pertolepe and predicting that he will eventually be revealed as a man of royal blood.

During the night, Pertolepe secretly orders thirty knights to guard Gareth against treachery. The following morning he escorts Gareth and Lynette through the forest and promises that he and his knights will answer whenever Gareth summons them. Gareth instructs him that, when called, they must present themselves to King Arthur.

Pertolepe later fulfils that promise and appears before Arthur with a company of knights. At the wedding of Gareth and Dame Lionesse, he arrives with thirty knights, performs homage to Gareth and requests the office of chamberlain for the feast. King Arthur subsequently makes Sir Persant of Inde and his two surviving brothers, Pertolepe and Perimones, Knights of the Round Table and grants them lands.

Much later in Malory’s narrative, Pertolepe and Perimones are listed among the knights killed during Sir Lancelot’s violent rescue of Queen Guinevere. Pertolepe’s full story therefore moves from family vengeance, through defeat and reconciliation, to recognised service within Arthur’s fellowship and eventual death during the collapse of the Round Table.