Karl Julius Alexander (Lex) Thoenes was born on April 4, 1907. He graduated from the Technische Universität München (Technical University of Munich) (1930) with a Dipl.-Ing. (Master's) degree in mechanical engineering.

As a student, Thoenes participated in the Akademischen Fliegergruppe München (Akaflieg München). The Akaflieg is a group of students interested in conducting research on and building gliders and light aircraft. Many members of this group eventually become engineers in the German aerospace industry. Thoenes lead the redesign and reconstruction of the Münchner Kindl for the 1927 sailplane competition in the Rhön, where he piloted the Münchner Kindl and won first prize in the Training Class. The following year (1927-1928), Thoenes was in charge of the next sailplane, the Kakadu, which he also piloted during the 1928 competition. In addition to his aviation activities as a student in Munich, Thoenes became a mountain climber and was chosen to be a member of the 1929 German Expedition to Kanchenjunga in Sikkim, India.

After graduation, Thoenes accepted a three year job (1930-1933) as the Technical Director of the Rossitten Sailplane School of the Rhön-Rossitten-Gesellschaft (RRG) in East Prussia. His duties included maintenance, serving as a sailplane tow-pilot and building a training sailplane which he named "Alexander der Kleine." Incidentally, Alexander Lippisch was also working at the RRG at the same time, but on the staff of the aerodynamics and design department.

Thoenes attended a test pilot school in Berlin (1933) and was assigned (1934) to the German Air Ministry flight Test Center at Rechlin where he remained, aside from wartime interruptions, until his death (September 25, 1944).

The collection (2009) contains an abbreviated biography (from Chapter 3) of Alexander Thoenes, written by his son, Jürgen Thoenes. The abbreviated biography chronicles Thoenes' Akademische Fliegergruppe (Akaflieg) endeavors while at the Technical University of Munich. In the biography, the author incorporated comments on the sailplane contests made by Alexander Lippisch in three of his technical reports (1927-1929) and published in the Zeitschrift für Flugtechnik und Motorluftschiffahr (ZFM). The biography is saved on a CD in a PDF (Version 1.3) format, and a printout of the biography is also in the collection.

For a related collection, see the Alexander Lippisch Papers (MS 243).