Markus Holler’s most outstanding contribution to H.E.S.S. was the tremendous work he did in the development of a new paradigm, namely the Run Wise Simulations. This new simulation framework not only paves the way towards improved control of systematic effects, thereby opening new science cases such as the measurement of the extension of the Crab Nebula, but will very likely have a very large impact on the future of VHE gamma‐ray astronomy in general. Markus Holler was hired primarily for an ambitious project aiming at measuring the Galactic Diffuse Emission in VHE gamma‐rays. This is very challenging and requires in particular to significantly improve the understanding the of instrumental background systematics, and thus to develop new background determination/subtraction techniques. A more precise simulation of the instrument was quickly identified as the central element in these investigations. Markus led this task with enthusiasm, pertinacity and efficiency, and with a great care of precision. He successively incorporated many effects such as non‐operational pixels, actual calibration, effect of telescope dead‐time on event multiplicity, and actual tracking of the telescopes. He devoted a huge amount of work on the comparison between Monte Carlo and real data. At the end, we have now a much more precise simulation of the instrument, which opens up new possibilities previously out of reach: the almost perfect understanding of the PSF, for instance, enables extension measurements with great confidence (e.g. Crab Nebula). Last but not least, the success of this approach raised large interest in the community, as future instruments such as CTA will probably have to adopt Run Wise Simulations for optimal scientific return. In addition, Markus is serving as deputy‐convener of the Analysis & Reconstruction WG. He provided many cross‐check analyses and contributed to an incredibly large number of tasks. He is also very well considered in the collaboration for his kindness, his abilities to share his work and willingness to help.