Anthony James Leon 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, Uruguay and Paraguay under the African National Congress government from 2009 to 2012.

The Leader of the Opposition in South Africa is the leader of the largest political party in the National Assembly that is not in government. The House of Assembly was the most important House from 1910 to 1994 and the National Assembly from 1994. The leader of the opposition acts as the public face of the opposition, leading the Official Opposition Shadow Cabinet and the challenge to the government on the floor of Parliament. They thus act as a chief critic of the government and ultimately attempt to portray the opposition as a feasible alternate government.