Some facts of his life and career can be easily summarized as follows. Born on May 31, 1964 in Graz, he studied at the Graz University of Technology, and got a PhD under Franz Rendl in 1991 with a thesis entitled 'Geometric clustering, Reconstruction and Embedding Problems: Combinatorial Properties and Algorithms'. He became a professor at the University of Twente (the Netherlands) in 2001, and joined TU/e as a professor in Combinatorial Optimization in 2004. In 2016 he moved to RWTH Aachen. During his time at TU/e, he supervised around ten PhD-students.
Describing the impact of his career on the field is not so easily summarized. He was present in almost every field within theoretical computer science. Social choice, bibliometrics, algorithms (especially online), approximability, computational geometry, and of course, one of his prime loves: computational complexity. His talent to see connections between different problems was amazing. His ability to distill the essentials, and then write it up in a way that it all seemed natural was uncanny. And his drive and enthusiasm to distinguish easy from hard, was absolutely infectious. The math and computer science department of TU/e owes him a lot - we are very grateful for his time spent at the department. His friendliness combined with a deep mathematical curiosity has been a source of inspiration for all around him. That spirit is still part of the department.
He was on the program committee of an enormous number of conferences, he was program chair of ESA1997, MAPSP2005, IPCO2011, EURO2009, and he was on the board of a dozen journals among which OR Letters. He set up, and maintained the P-versus-NP page, a vintage Gerhard-style set of webpages that discusses attempts to settle the P=NP question. To say that he contributed to the Christmas puzzle (Advents Kalender) is an understatement, he single-handedly ensured the existence of it. And there is much, much more to be said.
Above all, he could listen - he was able to identify truth in your unstructured words. And then he'd write the paper, faster than you thought was possible. We will miss his presence at conferences, his revealing questions at presentations, his modest smile when the result was discovered, and his knowledge. He knew about the origins of the term NP-complete, he knew results from faraway times in obscure journals; he also knew about the ideal composition of a darts board, and he knew his soccer.
We remember Gerhard as a friendly colleague with a formidable drive for science. We are shocked by his far too early passing and our thoughts are with those he left behind.