Mueller, who also set up the RAG foundation, stepped down as chairman of RAG and Evonik's supervisory board last year due to ill health.

The foundation is a majority shareholder in Evonik and was set up by Mueller to help deal with the costs of winding down the hard coal mining industry in western Germany and to try to reduce the impact on the Ruhr industrial region.

He also served as economy minister under Social Democrat Chancellor Gerhard Schroeder.

(Reporting by Vera Eckert; Editing by Mark Potter)