The general purpose of this thesis was to explore the different roles enacted by entrepreneurs when developing their firm in the market. In their daily attempts to develop their firm, entrepreneurs "wear many different hats" because they are involved in multiple situations which require their interaction with different networks of social relationships (i.e. customers, employees, suppliers, investors). Through this research, we attempt to make three related and distinct contributions: (1) identification and definition of different roles enacted by entrepreneurs within their firm; (2) development of a measurement scale for the different roles entrepreneurs enact within their firm; and (3) proposal of a model explaining the relationship between entrepreneurs' roles, Entrepreneurial Orientation, and firm performance.The thesis is presented in the form of three related papers. Paper 1 focuses on the qualitative study of the self-reported perceptions, behaviors, and attitudes that entrepreneurs relate to their efforts of developing their firm in the market. Through in-depth interviews and following thematic analysis methodology, we identified and analyzed patterns within the qualitative data. Conceptualizing the entrepreneurial firm as a proximate social structure that represents a context in which the entrepreneur establishes close relationships and thus enacts role identities, we identify and define seven different sets of behaviors or roles. In addition, we propose a conceptual framework to explain the entrepreneurs' agency within their firm.Based on the previously identified and defined roles, in Paper 2 we develop the measurement scale for the entrepreneurs' roles. The items generated from the literature review and the in-depth interviews were evaluated for content validity by a group of serial entrepreneurs. A pilot test was then conducted with a network of international entrepreneurs (N=55), followed by a pre-test using an online panel of U.S. entrepreneurs (N=157) who were owners and managers of a running business that had paid salaries to the owner(s) for more than two years. Finally, the main study (N=202) was conducted utilizing the same sampling frame as the pre-test. After Confirmatory Factor Analysis and measure validation, we propose a seven-construct measurement model for the roles that entrepreneurs enact within their developing firm.In Paper 3, following the development of the measurement scale, we explore the links between the roles enacted by entrepreneurs, Entrepreneurial Orientation, and firm performance. Understanding Entrepreneurial Orientation as a way in which entrepreneurs behave when creating and developing their firm, we propose a model in which Entrepreneurial Orientation mediates the relationship between entrepreneurs' enacted roles and the performance of their firm. Our findings suggest that Entrepreneurial Orientation mediates the relationship between at least five roles enacted by entrepreneurs and firm performance. The influence of several of the enacted roles of entrepreneurs on Entrepreneurial Orientation suggests that the entrepreneur's agency, facilitated through the use of roles, needs to be taken into account as an antecedent in a model of entrepreneurial strategic orientation and firm performance.