Driven largely by societal discourse regarding the underrepresentation of African American males pursuing science, technology, engineering and mathematics (STEM) majors, careers and professions, it becomes salient to understand how African American males experience mathematics in K-12 public schools in relation to their mathematics identity development. Mathematics teachers play a critical role in developing African American male mathematics identity. Utilizing an integrative lens of identity, this study examined one teacher's mathematics identity development and its influence on her teaching of students. The analysis focuses on how mathematics teachers' identities shape mathematics instruction for African American students, ultimately impacting their emerging identities as learners of mathematics. I argue that foregrounding teacher identity in mathematics within an integrative lens of identity can enhance our current understanding of how K-12 mathematics instruction impacts career trajectories in STEM for African American students.