Guillaume Ragutel de Montfort

Guillaume de Montfort (died 27 September 1432, Siena, Italy) was a 15th-century French cleric, Bishop of Saint-Malo and cardinal.

Biography Montfort was born in Dinan, Brittany, the son of , lord of Montfort and Gaël, and Isabeau de la Roche-Bernard, lady of Loudéac (died 1400).

Entering the church at a young age, Montfort was appointed protonotary apostolic and Archdeacon of Dinan. Named Bishop of Saint-Malo on 13 October 1423, the following year he took command of the military forces of Brittany, and advanced on the English besieging Mont Saint-Michel, forcing them to withdraw.

Pope Martin V offered Montfort the bishoprics of Saint-Brieuc in 1424, and of Dol in 1430, but he refused both.

On 29 May 1424, he demonstrated his opposition to John V, Duke of Brittany, who was constructing a dungeon at the château of Saint-Malo, by throwing a stone. Thus he affirmed his rights over the territory, which the duke had appropriated.

He was created a cardinal in pectore by Pope Martin V on 8 November 1430. He was henceforward known as "the cardinal of Brittany".

While visiting Rome, he travelled secretly to the Council of Basel, against the pope's wishes. He died suddenly en route, possibly poisoned, on 27 September 1432, and was buried in the church of the Cordeliers in Siena.