Guglielmo Grasso, sometimes anglicized William Grassus[a] (died 1201), was a Genoese merchant, pirate and admiral.
As a trader serving Genoa's leather sector, Grasso was active in the eastern Mediterranean. Around 1192, he turned to piracy in Byzantine waters. A string of high-profile attacks—including the slaughter of three embassies (two Byzantine, one Ayyubid) and unarmed civilians in Rhodes—forced Genoa to disown him. He reappeared in the service of the Emperor Henry VI in the Kingdom of Sicily in 1194 and was rewarded with the County of Malta and the rank of ammiratus (admiral). He lost his county in an uprising in 1198 and briefly returned to Genoa. He was back in Sicily in 1199 taking part in the civil war over the regency for Henry's young heir. After a change of allegiance, he was captured by his former allies and imprisoned in 1200. Genoese efforts to procure his release were rebuffed and he died in prison. Nevertheless, his son-in-law managed to succeed him in Malta.
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