Who is Kay from Arthurian Romances and what is their importance?

Kay is a knight in King Arthur's court. He is described as haughty and arrogant, always insulting and provoking the other knights. When Meleagant offers a challenge to King Arthur's court, Kay accept its. He loses then loses the challenge and is imprisoned with Queen Guinevere. When Lancelot arrives to rescue the queen and indulges in a night time rendezvous, Kay is accused of sleeping with Queen Guinevere.