Gawaine (or Gawain, Gwalchmai, or Walwen) is one of the
knights of
King Arthur's
Round Table. He is usually listed as Arthur's
nephew, since his parents are
Lot of Orkney and
Morgause, Arthur's half-sister through their mother
Igraine. (
Geoffrey of Monmouth names Gawaine's mother as Anna, though.) Gawaine is the leader of the Orkney family, being the oldest brother of
Agravaine,
Gaheris,
Gareth, and their half-brother
Mordred. He was knighted at Arthur and
Guinevere's wedding, and is often listed as second only to Lancelot in fame and status among Arthur's knights.
French stories tend to cast Gawaine as just one of the Round Table knights, while English stories are more likely to have him as the major figure (such as Sir Gawain and the Green Knight, among others). Different stories have Gawaine marrying different women.
Older works paint him as courteous, gallant, and smart, but Gawaine is often portrayed in more recent works as stubborn, blunt, hot-tempered, and proud. He is always very brave and loyal, to Arthur and to his brothers particularly (and very bitter toward Sir Lancelot who accidentally killed two of them). His quest for revenge against Lancelot was one of the factors that helped dissolve the Round Table. Howard Pyle describes Gawaine this way: "For indeed, though Sir Gawaine was at times very rough and harsh in his manner, and though he was always so plain-spoken that his words hid the gentle nature that lay within him, yet, under this pride of manner, was much courtesy."
Sources:
http://www.lib.rochester.edu/camelot/gawmenu.htm
http://www.camelotintl.com/legend/gawain.html
http://www.geocities.com/s_perrelli/ebooks/pyle/pyle_b2p3.html
http://www.bulfinch.org/tales/chiv05.html
http://www.uidaho.edu/student_orgs/arthurian_legend/quests/monsters/awandw.html