Donal Conor David Dermot Donat Cruise O'Brien (3 November 1917 – 18 December 2008), often nicknamed "The Cruiser", was an Irish diplomat, politician, writer, historian and academic, who served as Minister for Posts and Telegraphs from 1973 to 1977, a Senator for Dublin University from 1977 to 1979, a Teachta Dála (TD) for the Dublin North-East constituency from 1969 to 1977, and a Member of the European Parliament (MEP) from January 1973 to March 1973.