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William Keolaloa Kahānui Sumner, Jr. (c. 1816 – May 25, 1885) was a high chief of the Kingdom of Hawaii through his mother's family; his father was an English captain from Northampton. Sumner married a Tahitian princess. Aided by royal family connections, he became a major landowner and politician in Hawaii.
After contracting leprosy in 1877, by law Sumner was exiled to Kalaupapa, Molokaʻi. He served there as luna (superintendent) of the leper colony from 1878 to 1884. He died of leprosy in a Honolulu hospital in 1884.