Sidney Charles Cooke (born 18 April 1927) is an English convicted child molester and suspected serial killer serving two life sentences. He was the leader of a paedophile ring suspected of murdering up to twenty young boys in the 1970s and 1980s. Cooke and other members of the ring were convicted of three killings in total, although he was only convicted of one himself. Cooke was nicknamed Hissing Sid by colleagues, and was described by The Guardian newspaper in 1999 as "Britain's most notorious paedophile".