http://en.wikipedia.org/wiki/List_of_people_who_have_mysteriously_disappeared

1412 - Owain Glynd?r, the last native Welsh person to hold the title Prince of Wales, instigated the Welsh Revolt against the rule of Henry IV of England in 1400. Although initially successful, the uprising was eventually put down, but Glynd?r disappeared and was never captured, betrayed, or tempted by Royal Pardons. Nothing certain is now known of him after 1412, but efforts to identify his grave continue.