After a humanistic school education, Gerhard Haerendel chose to study physics with the intention of becoming a researcher in astrophysics. Commencing as graduate student with Ludwig Biermann, the leading astrophysicist of that time, he was soon "handed over" to Arnulf Schlüter, Germany's foremost plasma theorist, as thesis advisor. Shortly afterward, the Max Planck Institute for Physics and Astrophysics in Munich under Werner Heisenberg set up a research group for space research under Reimar Lüst, who hired Haerendel as young theorist supporting the experimental program consisting of seeding visible barium plasma clouds in space. In 1969, he was appointed leader of this experimental program and, three years later, became co-director of the Max Planck Institute for extraterrestrial Physics in Garching/Germany. He led this program from simple sounding rocket experiments to international projects involving combined active and diagnostic payloads focusing on specific phenomena such as plasma instabilities like equatorial spread F, magnetosphere-ionosphere coupling, auroral acceleration, and finally to the ultimate goal of creating two artificial comets in the solar wind, so far the only experiments ever of this kind.  The latter step of this program was enabled by his group having acquired the competence to build entire satellite payloads. This led naturally into participation in the global exploration of the magnetosphere and its interaction with the solar wind.  The missions were conceived and carried out as national programs under the control of the his institute, however with strong international cooperation and support by NASA, ESA, and the Swedish Space Corporation. He was strongly involved in the interpretation of the data obtained and the development of pertinent theories. He played a role in the creation of three major research institutions, the European Incoherent Scatter Radar (EISCAT), the Skinakas Observatory on the Island of Crete, and the International University Bremen (IUB), now Jacobs University. He was involved in the evaluation of Eastern German Academy institutes in geo-astrophysics and, as a follow-up, created an external laboratory of his Max Planck Institute in Berlin for a duration of five years. He served as chair or member of various advisory committees including the European Space Science Committee (ESSC) of the European Science Foundation and, for eight years, as president of the Committee on Space Research (COSPAR). After retiring from his last job as the founding dean of the School of Engineering and Science of the IUB, he devoted his time to developing theories of geomagnetic processes, in particular the formation of auroral arcs and the transfer of energy from thegeomagnetic tail to the magnetosphere, and of various phenomena on the active sun.