William Frangipani

William Frangipani (Guglielmo; died 1337) was a Roman Franciscan of the Frangipani family who held the see of Patras as Latin Archbishop from 1317 and ruled its barony as a virtually autonomous lord.

His ties ran to Venice: in 1321, as Byzantine forces pressed Achaea, he led a failed bid to hand the principality's remains to the Republic, and in 1336 he became a Venetian citizen. In 1329, when Prince John of Gravina left the Morea for Italy, he was named bailli, the first cleric to hold the post, and settled disputes between the feudal lords until 1331.

After 1330 he repeatedly excommunicated the Catalans of Athens. When Bertrand des Baux became bailli in 1336, William refused homage to the prince and relations soured. He died in 1337, and Bertrand's siege of Patras failed to bring the archbishopric back under control.