The Green Knight
Pertolepe was the second of four brothers whom Gareth encountered on his way to fight Sir Ironside at Castle Dangerous; the others were Percard, Perimones, and Persant. Pertolepe's trappings were "all in green, both his horse and his harness." On seeing Gareth in the black armor of his brother Percard, and learning that Gareth had slain Percard, the Green Knight rode unto a horn that was green, and it hung upon a thorn
and there he blew three deadly notes, and there came two damsels and armed him lightly.
And then he took a great horse, and a green shield and a green spear.
(Although each of the four brothers is connected with a color, and although Pertolepe should not be confused with the more famous Green Knight of Gawaine's adventure, Bercilak de Hautdesert, the above passage may suggest a common origin in the roots of legend for the two.)
After his defeat, Pertolepe pledged himself and thirty knights to be at Gareth's service, lodged Gareth and Lynette for the night, and, true to Gareth's command, showed up along with his surviving brothers at Arthur's court that Pentecost.
He made a good showing in Dame Lyonors' tournament at Castle Dangerous, and returned to court about the time of Gareth's wedding, bringing his thirty knights and obtaining the favor of acting as Gareth's chamberlain at the high feast of Michaelmas. Soon thereafter he was elected to the Round Table.