William I, Marquis of Namur

William I, Marquis of Namur, the Rich, (1324 – 1 October 1391) was Count of Namur from 1337 until his death.

He was the fifth son of John I and Mary of Artois. Because his four elder brothers all died childless between 1333 and 1337, he still became Marquis of Namur.

William participated in the Hundred Years' War on the side of the English. Despite this, Namur itself remained at peace, except for a revolt of the weavers in 1351. He was defeated and taken prisoner in the Battle of Baesweiler in 1371.

Thanks to the fortune, first of his mother and then of his wife, William was able to buy several territories which enlarged the Marquisate. In 1362 he obtained from Charles IV, Holy Roman Emperor that Namur depended directly from the Holy Roman Empire and ceased to be a vassal of the County of Hainaut. He also developed the mining and forging industries, as well as commerce.

He first married on 13 February 1348 with Jeanne of Hainault, daughter of John of Beaumont and Margaret of Soissons. Jeanne died 2 years later form the Black Death without children.

William remarried in March 1352 with Catherine of Savoy, daughter of Louis II of Savoy, baron of Vaud, and Isabella of Châlon. They had 3 children :

• William II (1355-1418), Marquis of Namur
• John III (?-1429), last Marquis of Namur
• Marie (?-1412), married in 1370 Guy II de Blois-Châtillon and in 1405 Pierre de Brabant, Admiral of France.

William also had several illegitimate children.