This study is a linguistic ethnographic investigation of teacher identities in an English for Medical Purposes (EMP) classroom at one of the medical colleges in the kingdom of Saudi Arabia. It focuses on the discursive shifts of teacher identities in his classroom interactions. An eclectic qualitative methodology that incorporated principles of Linguistic Ethnography was employed in this study. Classroom observation was the main method for data collection. When necessary, an informal conversation with the teacher was carried out after classroom observation to obtain further clarification of what had happened during the observation. The class was observed for 13 times during the first semester of the academic year 2019/2020. Five salient identities were constructed by the teacher: the expert, the counsellor, the student, the storyteller and the controller. These identities were found to be fluid and multiple and became temporarily salient in different classroom interactions. The teacher mediated classroom discourses by constantly shifting relationships and identities along the inclines of power. This study concludes that teacher's discursive identities portray positive self-image and account for students' active engagement and involvement in the learning process.