Dieter Althaus is a German politician of the Christian Democratic Union.
Althaus was teaching Physics and Mathematics at the Polytechnic Secondary School in Geismar, Thuringia, from 1983 to 1989, where he became deputy headteacher in 1987.
Since 1985 Althaus has been a member of the CDU, remaining with the party as it transformed itself from a loyal supporter of the GDR's ruling Socialist Unity Party of Germany to a loyal supporter of the West German party of the same name with which it merged in 1990 shortly after German reunification. In 2000 he became chairman of the CDU in Thuringia. Since 1990 he has been a member of the Thuringian Landtag.
In 1992 he became a member of Bernhard Vogel's cabinet as minister of culture and education.
On 5 June 2003 he was elected Minister-president of Thuringia; he succeeded Bernhard Vogel, who had resigned for reasons of age. As Minister-President he served as President of the Bundesrat in 2003/04.
Althaus is married to Katharina and has two children. He caused a skiing collision in Styria, Austria on January 1, 2009, in which he suffered severe injuries. Althaus was skiing down an expert run, but wandered onto an easy slope, where he was skiing in the wrong direction, whereupon he and a 41-year-old Slovak woman collided. The woman subsequently died from her injuries. Althaus was wearing a skiing helmet, while the woman was not. Althaus was fined €33,300 for negligent homicide.