Gawain (/ɡəˈweɪn/; Welsh: [ˈɡawain]), also known as Gawaine or Gauwaine, among various other forms and spellings, is King Arthur's nephew and a Knight of the Round Table in the Arthurian legend. Under the name Gwalchmei, he appears very early in the legend's development, being mentioned in some of the earliest Welsh Arthurian sources. As Gawain, he appears in Latin, French, English, Dutch, German and Italian literature, notably as the protagonist of the story of Sir Gawain and the Green Knight. Other tales of Gawain include Historia Regum BritanniaeRoman de BrutDe Ortu WaluuaniiDiu CrôneThe Awntyrs off ArthureL'âtre périlleuxLe Chevalier à l'épée, and The Weddynge of Syr Gawen and Dame Ragnell, as well as the works of Chrétien de Troyes and the prose cycle Lancelot-Grail.

Gawain is one of a select number of Round Table members to be referred to as one of the greatest knights and closest companions of King Arthur. He is usually the son of Arthur's sister Morgause (or Anna) and King Lot of Orkney and Lothian, and his brothers or half-brothers are Agravain, Gaheris, Gareth, and Mordred. He is often portrayed as a formidable, courteous, and also a compassionate warrior, fiercely loyal to his king and family. As such he is a friend to young knights, a defender of the poor, and as "the Maidens' Knight", a defender of women as well. He has a horse named Gringolet, uses the sword Excalibur, and his sons may include the "Fair Unknown", Gingalain. One recurring theme of later versions of Gawain's legend is his friendship with Lancelot, who eventually becomes his bitter enemy. Gawain's usually glowing portrayals are diminished in the Lancelot–Grail Cycle in favour of Lancelot and especially Galahad, and his character even turns markedly ignoble in the Post-Vulgate Cycle.

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