Sir Stephen Rothwell O'Brien, (born 1 April 1957) is a British politician and diplomat who was the United Nations Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator. O'Brien assumed office on 29 May 2015, succeeding Valerie Amos.He was formerly a Member of the United Kingdom Parliament (MP), representing Eddisbury. He was first elected in a by-election in July 1999, after Alastair Goodlad was made British High Commissioner in Australia by Tony Blair and thus had to leave Parliament. A member of the Conservative Party, within the Conservative-Liberal Democrat Coalition he was appointed as the Parliamentary Undersecretary of State in the Department for International Development. In September 2013 he became the Prime Minister's Envoy to the Sahel, encompassing nine countries across North and West Africa.