William Herle (died 1589) was an Englishman who led a double life as a respectable Member of Parliament and county sheriff, and well as a privateer and spy who was imprisoned in the Marshalsea prison in 1571. He became known for his part in Elizabeth I's intelligence network inside the jail, smuggling letters to William Cecil, Lord Burghley, about people involved in the so-called Ridolfi plot, a Roman Catholic plan to assassinate the Queen and replace her with Mary, Queen of Scots.