The Hereward the Wake reference article from the English Wikipedia on 24-Apr-2004
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Hereward the Wake

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Hereward the Wake was an outlaw, who, according to legend, roamed the Isle of Ely leading popular opposition to William the Conqueror. According to the 15th century chronicle, Gesta Herewardi, by Ingulf of Croyland, he was pardoned by William, but not before he had laid waste to the city of Peterborough with Viking assistance.

Some of the legends about Hereward were incorporated into the legends about Robin Hood. Charles Kingsley's novel of 1865 is a highly-romanticised account of Hereward's exploits, and makes him the son of Earl Leofric of Mercia.