The Harring of the North by William the Conqueror

The harring of the north famously involved a character called edgar the etheling, who is this figure who appears to have been appointed an heir to edward the confessor. He's proclaimed by some as the new king of england, and then william comes along and honestly stamps him himself on the scene. And i think perhaps it's a huge over reaction that shows william's insecurity and fear in the face of what could be a very serious threat to him. Then let's turn to herwad. What do the sources tell us about his life beforehe poms against william?