RENE S. SPIEGELBERGER founded the Spiegelberger Art Foundation. He is a member of the board of trustees of the Museum Schloss Moyland, which owns the world's largest collection of Joseph Beuys’ work. Spiegelberger regularly gives lectures on the art market. He also authors numerous specialist articles on art and works as an exhibition curator. CLAUS VAN DER OSTEN is a collector of artist posters living in Hamburg.