Patrick Bartholomew `` Bertie '' Ahern ( ; born 12 September 1951 ) is a former Taoiseach of Ireland leader of Fianna FÃ il , the Irish Republic 's largest political party . Patrick Bartholomew `` Bertie '' Ahern ( born 12 September 1951 ) is a former Irish politician who served as Taoiseach of Ireland from 26 June 1997 to 7 May 2008 .