William I de la Roche

William I de la Roche (French: Guillaume, † 1287 ) was a Duke of Athens from the family la Roche. He was a younger son of Duke Guido I of Athens and the Agnes de Bruyeres.

From his late father in 1263, he received Livadia as a separate barony. After his older brother, Duke John I 's death, he followed them as Duke.

Wilhelm recognized Charles of Anjou as his liege lord and looked at peace with his brother Emperor Michael VIII Palaiologos as having lapsed. The Emperor then ravage through his generals Licario Boeotia and Attica. Wilhelm joined the Angevin alliance against Byzantium and prepared for the offensive against the Angevins Konstantin Opel ago. But when in March 1282 broke the Sicilian Vespers, remained from the attack. The collapse of the Angevin rule, the Frankish princes of Greece lost its last great post. Only the inaction of the new Emperor, Andronikos II, Athens saved from a Byzantine counter-attack.

1285 William was employed by Count Robert II of Artois, Regent of the Angevins, as Bailli in Achaia. There he ordered the relations and assured the country through the construction of new castles, as Dimatra. He died in 1287.

William was married to Helena Angelina († 1294/95 ), a daughter of John I Angelos Despot of Thessaly. The only child together was the new Duke Guido II († 1308), for which his mother took over the guardianship.