Anthony James Leon (born 15 December 1956) is a South African politician who served as leader of the opposition from 1999-2007 as leader of the Democratic Alliance (DA). He led the DA from its inception in 2000, until his retirement from leadership in 2007. Before that, he led the Democratic Party from 1994. He is the longest serving leader of the official opposition in parliament since the advent of democracy in 1994. Although still a member of the DA, he served as the South African Ambassador to Argentina under the ANC government from 2009 to 2012.