The historic development of technical catalysts at the Leuna chemical site is shown in a series of four articles. Although the research resulted in more than 300 patents, this paper does not intent to constitute a formula for success for the development of new catalysts. Instead, it aims at highlighting the remarkable and internationally recognized accomplishments of the Leuna R&D teams in the field of catalyst and process development from the 1950s until the late 1980s. In addition to the the economic value of hundreds of millions of Mark (the GDR currency), an significant result of these R&D activities was a much more elaborated concept on the properties and mode of action of technical catalysts. Part 4 looks at hydrocracking catalysts and the corresponding industrial processes developed in the former GDR.