The philosopher Michael Theunissen died on April 18, 2015.  He studied in Bonn and Freiburg and defended his much-cited habilitation thesis Der Andere: Studien zur Sozialontologie der Gegenwart (The Other: Studies in Contemporary Social Ontology) in Berlin in 1964.  He was professor in Berne, then Heidelberg and Berlin, where he was colleague alongside figures such as Ernst Tugendhat, Dieter Henrich, and Hans-Georg Gadamer.  The main philosophical figures and themes he dealt with were Kierkegaard, Hegel, phenomenology, social philosophy and ancient philosophy. There is an obituary (in German) here.

(Thank you to Sebastian Luft for this information and for help writing this post.)