The author reports on a case study investigating how one nonnative English-speaking teacher (NNEST) struggled to claim professional legitimacy as a university-level ESL writing instructor. Using Vygotskian sociocultural theory (Vygotsky, 1978, 1986; Wertsch, 1985) and Bucholtz and Hall's (2005) indexicality principle, the author explores the relationship between the participant's professional self-concept and teaching practice as well as how in-service professional development experiences impacted his thinking, discourse, and action. The findings suggest that coursework and professional development addressing the native speaker myth can provide NNESTs with mediational tools through which to reimagine themselves as legitimate speakers and professionals in English Language Teaching (ELT). (Contains 1 footnote.)