Product Owners have an important role in the agile software development process. While the description of the Product Owner role heavily depends on its particular agile framework, the application of a single development framework is seldom in practice. In fact, customized hybrid development approaches, where frameworks/methods are tailored or combined with others, are state of the art. Although it is common knowledge that processes need to be tailored to project needs, as they become, otherwise, a project risk - the tailoring of the Product Owner role has been neglected in research so far. Consequently, there is a lack of knowledge about how to tailor the Product Owner role to hybrid development environments. As this knowledge gap can put projects in a hybrid environment to a risk, the goal of this thesis is to close this gap. To achieve this, a knowledge-base of Product Owner peculiarities needs to be established and consolidated with knowledge from the area of Software Process Tailoring. To generate the knowledge-base of the Product Owner peculiarities, a number of case studies as well as a systematic mapping study was conducted to identify Product Owner tasks, characteristics and structures in hybrid development environments. This resulted in the identification of 13 frequently conducted tasks, 6 favorable characteristics and 12 different structures of Product Owners that apply in hybrid development environments. From the area of Software Process Tailoring, 14 influencing factors on the Product Owner role were extracted along with its respective action items. The consolidation of this knowledge results in a catalog which combines the influencing factors, the Product Owner tasks, characteristics & structures as well as the respective implications on the Product Owner role according to the research results of this thesis. Based on this catalog, any project environment can be assessed and distinct recommendations for a tailored Product Owner role can be deduced. Overall, this thesis generated 84 different recommendations on how to tailor the Product Owner role to a particular hybrid development. With this, so far missing knowledge was gained to systematically support the tailoring of the Product Owner role to hybrid development environments and thus, to support projects to complete successfully. To share the gained knowledge to other researchers as well as practitioners, this thesis also provides an expert system in the form of a proof of concept web-application. The so-called Hybrid Product Owner (short: HyPrO) Expert System represents the research results of this thesis. Its user-friendly interface enables the user to assess the project environment and displays the respective recommendations. The HyPrO Expert System validated the results of this thesis, as it surpassed human experts by providing more comprehensive recommendations in a comparative case study.