Over many centuries, humans have been tuning metals to create desirable properties. Typically, it comprises the addition of rather low amounts of secondary elements to a main element. However, for the past decade and a half, a completely novel alloying strategy has come upon the horizon gaining significant importance. It involves the combination of multiple principal elements in high concentrations to create a new material type, termed high-entropy alloys. These new type of metals has already shown to possess extraordinary properties, going beyond those of conventional metal alloys. However, how crack initiation and growth can be prevented is key towards an improvement of fracture resistance when exposed to environments containing hydrogen. Hydrogen absorption followed by embrittlement can lead to the sudden and complete loss of the ductility of many high strength metallic materials. Hydrogen embrittlement is among the most complex and least understood material decay and damage phenomena. Finding a breakthrough in the development of hydrogen-resistant materials is required to realize a hydrogen-based society. So far, remarkable and promising results have been obtained on the role of hydrogen in these new type of alloys. This project aims to fundamentally understand the role of hydrogen on the deformation mechanisms to create an academic breakthrough on this complex and very novel topic with major opportunities to develop hydrogen-resistant materials.