Which king had a round table?

King Arthur, and the table is a late addition to a story that was already centuries old. It appears first in Wace's Roman de Brut in 1155, where the point is explicitly stated: a round table has no head, so no knight can claim precedence and quarrels over seating are avoided.

Arthur himself may or may not have existed. The earliest mentions are ninth-century Welsh sources describing a war leader fighting the Saxons around AD 500, with no round table, no Camelot, no Lancelot and no Holy Grail - all of which arrive through French romance writers in the twelfth and thirteenth centuries, several hundred years later. Lancelot is essentially an invention of Chretien de Troyes.

The object in Winchester Great Hall is a genuine medieval table and a genuine fake Arthurian relic: carbon dating and tree rings place it in the thirteenth century, and the Tudor rose and painted decoration were added under Henry VIII, who had it repainted with a portrait of Arthur that looks a good deal like himself. It is a real 700-year-old artefact created to support a claim that was already legendary when it was made.