Gaheris is a Knight of the Round Table in the chivalric romance tradition of Arthurian legend. A nephew of King Arthur, Gaheris is the third son of Arthur's sister or half-sister Morgause and her husband Lot, King of Orkney and Lothian. He is the younger brother of Gawain and Agravain, the older brother of Gareth, and half-brother of Mordred. His figure may have been originally derived from that of a brother of Gawain in the early Welsh tradition, and then later split into a separate character of another brother, today best known as Gareth. German poetry also described him as Gawain's cousin instead of brother.

The Knights of the Round Table are the legendary knights of the fellowship of King Arthur that first appeared in the Matter of Britain literature in the mid-12th century. The Knights are an order dedicated to ensuring the peace of Arthur's kingdom following an early warring period, entrusted in later years to undergo a mystical quest for the Holy Grail. The Round Table at which they meet is a symbol of the equality of its members, who range from sovereign royals to minor nobles.