Gillis Berthout (1175/80–1241), was a nobleman who fought on the Fifth Crusade, a hereditary chamberlain of the County of Flanders, and a Teutonic Knight.

The Berthout family held lands in Mechelen, and in the margraviate of Antwerp.

Around 1205 he married the Flemish noble widow Catherina of Bailleul, daughter of Gerard, viscount of Oudenburg.

On behalf of his wife and step-children, Gillis from 1206 held the hereditary chamberlaincy of Flanders and lordships of Leffinge, Lichtervelde, and Oudenburg.

From 1207 he served the interests of John, King of England, receiving regular payments from him and attending upon his court.