The greatest of King Arthur's knights of the Round Table, according the Celtic sources, Sir Gawain is Arthur's nephew. He is the eldest son of King Lot of Orkney and Arthur's sister Morgause, and he has at least three younger brothers: the knights Agravain, Gareth, and Gaheris. The most famous tale about Sir Gawain to modern readers is Sir Gawain and the Green Knight about a beheading contest between Gawain and a supernatural Green adversary, Sir Bercilak.

Gawain is a re-anglicization of the French spelling Gauvain, from the original Celtic Gwalchmei, which means "Hawk of May." Geoffrey of Monmouth called him "Gualguanus," and Wace called him "Walwein." Judging from the way medieval poets rhymed the name, "Gawain" was usually pronounced with the stress on the first syllable.