Harman Blennerhassett (blĕn´ərhăs´ət), 1765–1831, Anglo-Irish pioneer in America, an associate of Aaron Burr. Wealthy and gifted, he fell in love with and married his beautiful niece, Margaret Agnew. The couple was ostracized, and in 1796 Blennerhassett sold his estates and emigrated to the United States, where he bought (1798) part of what came to be called Blennerhassett Island. There he lived as a gentleman scholar interested in experiments in physics until Aaron Burr won (1805) his interest in Burr's plan of Western colonization. Blennerhassett advanced money to Burr. When President Jefferson proclaimed Burr's intentions traitorous, the local militia was mustered. Blennerhassett fled (Dec., 1806) down the river and was taken into custody. He was released after the government failed to convict Burr, but his fortunes were ruined. After a disastrous failure to recoup his losses on a Mississippi plantation, he attempted to practice law in Montreal, returned to England in 1822, and died on the island of Guernsey.