Oskar Lafontaine (born September 16, 1943) is a left-wing German politician who is a member of the Social Democratic Party (SPD). He studied physics at the University of Saarbrücken. From 1985 till 1998, he was Prime minister of the Saarland, and in 1998, he was appointed Federal Minister of Finance in the first government of Gerhard Schröder. On March 11, 1999, he resigned from all his official and party offices because, as he said, he did not like the "lack of cooperation" in the cabinet. More recently, he became known for his attacks on the current German government.

Lafontaine is married to Christa Müller and has got one son Carl Maurice (born 1997).

Lafontaine is a primary bogeyman of UK Eurosceptics, because for example, he has called for the prompt tax harmonisation of the European Union, the result of which would be a huge increase in the UK tax burden.