Haughty Knight of the Heath and His Damsel
Proud Knight of the Moor, Glade, and so on
Both the adjective and the place noun of his name vary with the translation. Perhaps I make a wild jump in identifying him with a knight who appears at a house where Lancelot is lodging for the night in the marches of Gore.
This man, looking more arrogant than a bull, rides up with one leg thrown jauntily over his charger's neck, asks for the fool who intends to cross the Sword Bridge, berates Lancelot for having ridden in a cart, and offers to ferry him across the water for the toll of his head, "if I feel like taking it". Lancelot rejects the offer, but humors the proud knight with an immediate battle on the nearest convenient field.
In this fight, both horses are soon killed. The first time Lancelot defeats his opponent, he offers him mercy on condition that he himself get into a cart. While the loser begs for mercy on any other terms, King Bademagu's daughter rides up and asks Lancelot, as a favor, to give her the head of the defeated knight, whom she calls the most perfidious traitor who ever lived.
Torn between the great knightly virtues of Pity - which bids him extend mercy to vanquished foes - and Generosity - which bids him to do the damsel the favor she asks - Lancelot lets his opponent rehelm, rearm, and fight again.
This time, Lancelot even puts himself under the handicap of fighting without moving from his original stance, but defeats him easily and lops off his head, presenting it to the delighted maiden.
My only reasons for identifying the unnamed knight killed by Lancelot with the one so briefly mentioned as being unhorsed by Erec is that Lancelot's challenger, whether or not as bad as the damsel claims, is certainly haughty, that the field whereon they fight happens to be a heath, that the knight of Eric and Enide was apparently not one of Arthur's, and that any new tag I might device Lancelot's opponent would probably include the element "Haughty" or "Proud" anyway.
The principal difficulty with the above identification is that a Haughty Knight of the Heath, alternatively called the Proud Knight of the Moor or of the Glade, reappears alive in Chrétien's last romance as the sweetheart of the damsel whom Percivale, on his very first adventure after leaving home, finds sleeping in a tent pitched in a woodland glade. Interpreting his mother's parting instructions rather liberally, Percivale roughly helps himself to the damsel's emerald ring, one of three waiting meat pasties and a silver cupful of wine, and an unwilling kiss from the maiden's lips. Returning to the tent after the intruder's departure, the Haughty Knight takes news of the ring, pasty, and wine in stride, but flies into fury when his damsel confesses the forced kiss. Clearly among those who believe "when a woman says no, she means yes", the Haughty Knight assumes that, if she is willing to admit a kiss, she must in fact have gone all the way with the stranger.
Punishing both her and, by some twist of logic, her unoffending horse, he makes her follow him with neither change of raiment for herself nor oats, veterinary care, nor new shoes for her mount, until he can find and decapitate the rude sranger. Nor does he content himself with wreaking vengeance on the particular unknown who committed the original offence: he slays any knight who stops to talk, however innocently, with his maltreated damsel along the way.
Some time later, immediately after leaving the Fisher King's castle, Percivale (now knighted and a little better acquainted with chivalric niceties) finds his cousin, the Fisher King's Niece, mourning her headless lover, who has just become the Haughty Knight's latest victim.
Percivale rides in pursuit, finds first the damsel and her horse, in very sorry state, and then the Haughty Knight himself, who appears in such a way as to suggest he has been using his poor sweetheart as bait. He retells the story to Percivale, who reveals his own identity as the youth of the tale.
Some mss. describe Trebuchet's Sword as breaking in the ensuing battle, but a deal of scholarly opinion considers this passage of about twenty lines as a later interpolation. Whether with Trebuchet's Sword or that of the Red Knight of Quinqueroi, Percivale defeats the Haughty Knight but grants his plea for mercy, charging him to take his lady somewhere she can rest and be healed, and then go to Arthur's court, tell the whole story, and give Kay the usual message that Percivale intends to come back and avenge the maiden whom the seneschal struck.
These directives the Haughty Knight carries out, with the observation that he really loves his sweetheart. It may have been considered sufficient amends in that era. When she is well enough, they find Arthur's court at Caerleon, where the knight presents his damsel to the Queen and relays his message. If the ususal pattern holds, they presumably join the court.