Egbert Brieskorn was professor of mathematics in Göttingen and Bonn and visiting professor at a number of foreign universities. Among mathematicians he was known for his fundamental contributions to the singularity theory of complex hypersurfaces. In Bonn he initiated the project "Felix Hausdorff - Gesammelte Werke"(10 volumes, 2001-2020) and served as head of the group of five editors responsible for the complete edition. For many years he worked on a biography of Hausdorff, which was to appear in the Hausdorff edition, though only about half of it was completed at the time of his death. Brieskorn was also the author of original and successful textbooks. He devoted decades of work to ecology and species conservation, for which he received the Cross of Merit on Ribbon of the Federal Republic of Germany. Walter Purkert was professor of the history of mathematics in Leipzig and visiting professor in Wuppertal. He later taught historyof mathematics in Bonn, where as a starting point for the Hausdorff editorial project, he published a finding aid with descriptions of the contents of Hausdorff's extensive estate. Thereafter, he served full-time as coordinator of the edition, overseeing the work of its editors, while contributing to a number of the volumes. After Egbert Brieskorn's death, he spent several years completing their Hausdorff biography, published in 2018 as Volume IB of the edition. Purkert also wrote a well-received biography of Georg Cantor. He is a corresponding member of the Académie Internationale d'Histoire des Sciences in Paris.