The author addresses the concept of the investor in investment protection law, which has so far played a secondary role compared to the examination of the concept of investment. Both are key terms in investment protection law. They define the personal and material scope of application and are prerequisites for access to international investment arbitration within the framework of jurisdiction ratione personae and ratione materiae. The definitions of these terms determine the answers to the two core questions of international investment protection law: Which investments and which investors should receive international legal protection and thereby be removed from national jurisdiction and elevated to the international level?.