Friedrich Robert (Fritz) Jaeger first studied mathematics and physics, and then geography and geology, at the universities of Heidelberg, Zurich and Berlin from 1899 to 1904. After passing an examination in Karlsruhe that qualified him to teach he accompanied a research expedition to East Africa and Egypt during 1906/7. His observations in East Africa were written up in some geographical papers. In 1909 he was admitted as a university lecturer in Berlin and in 1911 was appointed to teach German colonial geography and put in charge of the Colonial Division of the Geographical Institute. In 1913 he and his assistant Leo Waibel* were sent on a year long geological and geographical research expedition to German South West Africa (now Namibia) by the German colonial authorities. However, shortly after their arrival World War I (1914-1918) broke out and both were called up for military duty. After the German forces capitulated in July 1915 the territory came under South African control and during the rest of the war they were able to continue their research with interruptions. They were eventually deported to Germany in 1919, by which time they knew the territory very well and had acquired considerable expertise in locating groundwater resources.
Jaeger published the results of his observations on the geology and geography of the territory in some fifteen papers in German journals between 1920 and 1933. He and Waibel also published their geographical research as Beitraege zur Landeskunde von Suedwestafrika (2 vols, Berlin, 1920-1921). The work was a very thorough physical geography, with Volume 1 (80 pp) dealing with the surface configuration, hydrography and agriculture of Namibia as a whole and Volume 2 (138 pp) with several special regions, namely the Karstveld, Otavi Mountains, Grootfontein flats, inselberg country of Hereroland, and the region of the Swakop River.
Jaeger taught geography at the University of Berlin and became a member of the Leopoldina Academy of Sciences in 1926. In 1928 he was appointed professor of geography at the University of Basel, Switzerland, where he remained until his retirement in 1947. Over the years he was awarded medals by the Gesellschaft fuer Erdkunde zu Berlin (1918), the Gesellschaft fuer Erdkunde zu Leipzig (1921), and the Frankfurter Geographischen Gesellschaft. Among others he wrote the following books: Afrika. Physische Erdkunde (1925), Afrika. Geographie des Menschen und seiner Kultur (1925), Afrika. Der Lebensraum (1954) and Afrika. Mensch und Kultur (1954). In 1951 he donated the diaries of his travels in Namibia and other documents to the National Archives of Namibia, while some photo albums are held by the Namibia Scientific Society.