Drawing on a sociocultural understanding of identities as multiple and fluid, we investigate how six practicing teachers recruited their biographical resources in constituting their discourse identities in interviews. The South African context allows us to consider how systemic inequality shapes the identity resources available to teachers from diverse sociopolitical backgrounds. Using inductive thematic analysis, we found that racial positionality impacted the nature of the biographical resources at each teacher's disposal. The two teachers from advantaged backgrounds drew only on their own schooling experiences, whereas initial teacher education featured strongly in the identities of the other teachers. Two teachers chose to teach in schools serving poor communities, which contributed to their identities as teachers who give their students an escape from their home situations, in part because of resonance with the teachers' own home and schooling experiences. All six teachers' identities reflected both the discipline of science and a concern for student success, and evidenced the teachers' resourcefulness in using biographical resources to negotiate their identities in their current teaching contexts. The results suggest that science teacher educators would do well to pay attention to the diverse and idiosyncratic words that student teachers use to express their emerging identities, and the science teaching role-models available in their biographies. In addition, there is value in exposing student teachers to a range of teaching practices from which they can recruit material for their developing identities, rather than promoting a particular pedagogy.