Klaus Fredenhagen was born on 1 December 1947 in Celle, a German city in Lower Saxony. He graduated in 1976The doctoral thesis is from the University of Hamburg under the supervision of Gert Roepstorff and Rudolf Haag.. In 1985 he became a privatdozent and in 1990 a full professor at the second theory institute of the Hamburg University.He was the successor of Rudolf Haag's chair, who retired in 1987. See e.g. the historical overview Since 2013 he has been a professor emeritus and has continued to be active in research.
