Professor Dr. Klaus Töpfer is the former Executive Director of the IASS and Council Chair at Agora Energiewende. He is also the former Executive Director of the United Nations Environment Programme (UNEP) based in Nairobi and Under-Secretary-General of the United Nations (1998-2006). He was Federal Minister for the Environment, Nature Conservation and Nuclear Safety from 1987 to 1994 and Federal Minister for Regional Planning, Housing and Urban Development from 1994-1998.