Because Sir Gawain believed that King Arthur and Sir Mordred were poorly matched. Sir Gawain did not believe King Arthur could win the battle without help from Lancelot, and thus a month-long treaty would allow enough time for Lancelot to return and help usher King Arthur to victory over Mordred.
His own nephew, and son, Sir Mordred.
He was killed, or at least mortally wounded, at the battle of Camlann by his son and nephew, Sir Mordred.
In the story I have heard, Sir Mordred was supposedly Arthur's Son/Nephew. Merlin Prophesied that Arthur's son would kill him. Arthur sent Mordred out with 40 other babies to die afloat in a coracle out in the sea. Mordred was the only survivor, grew up in Lothe, and became a knight of the round table. He did fulfill his destiny. He killed Arthur while Arthur killed him. ( all this from I am Mordred by Nancy Springer)
Mordred stabs a knight in the back. He makes up lies about Lancelot. He kills Arthur.
Sir Galahad is Sir Lancelot's son. Sir Gwain is King Arthur's nephew. Sir Mordred is King Arthur's son.
No one actually knows who, but he was killed trying to retake Camalot from Mordred.
Sir Isac Newton discovered the law of gravity.
he climbed mt Everest
its because he lives in a house
You smell of poo
his brother is Sir Kay