Despite the acknowledged complexity of the expertise of teacher educators (Cochran-Smith, M. (2003). Learning and unlearning: the education of teacher educators. "Teaching and Teacher Education," 19, 5--28), there is limited research attending to what teacher educators need to know and how they develop this expertise. This self-study draws from multiple frameworks of teacher knowledge to investigate knowledge content, structure, and growth of a novice mathematics teacher educator-researcher (MTE-R) from her doctoral program into her third year of a tenure-track faculty position at a large southwestern United States university. Narrative inquiry was used to both examine past artifacts and create new data. The findings highlight how the multiple roles of MTE-Rs elicit different kinds of knowledge and how frameworks for studying mathematics teachers can be utilized for studying teacher educator-researchers. (Contains 8 figures.)