In the context of growing societal demand and interdependency, universities need to prioritize their "third mission" activities and balance them against core functions. Individual researchers too are faced with multiple external constituencies and various mechanisms for interaction. The degree, target, and mode of their involvement with societal actors must be considered in light also of high performance expectations concerning traditional teaching and research activities. In this study, we explore patterns of third mission involvement among 652 researchers at the Science and Technology Faculty, Aarhus University from 2009 to 2012 using register-based data. First, we collect 13 indicators of third mission involvement from the university register system PURE, and find that these can be organized in distinct sets. External interaction and knowledge sharing can take many shapes, but they appear to group together empirically in ways that reflect the external partners and mode of involvement. Secondly, we determine five clusters of researchers based on their third mission activities. The majority of researchers have limited engagement in any kind of third mission activities, while an almost negligible minority entertain activities across the board. The remaining researchers focus their engagement on one type of third mission activity: public sector service, industrial collaboration, or executive involvement. Finally, we explore the interrelatedness of third mission involvement and research performance. Researchers who work closely with industry perform extremely well in terms of both publication productivity and impact, while those primarily engaged with public authorities perform considerably below average. We contextualize the results and highlight the limitations of the study.