The principal investigator pursued four cycle 4 Compton Observatory guest investigator programs that investigated the nature and the origin of the high energy gamma radiation of active galactic nuclei. As a result of two Compton Observatory key projects, simultaneous multiwavelength observations from radio to TeV frequencies of these objects were made available. These obsevations were modelled in detail using the existing theories on the origin of nonthermal radiation from these objects. Moreover, the Dermer-Schlickeiser-model for the inverse Compton radiation from gamma ray blazars was developed further and used as input for the multiwavelength modelling. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(84,4) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany); DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Bonn (Germany)DEGerman