We explore how physical science doctoral students navigate their role identities throughout their graduate programme. Physical science doctoral students take on many academic roles in addition to the role of scientist, including researcher, educator, and student. When social expectations of roles become internalized, they become role identities. We examined doctoral students' academic role identities as a complex system to unpack factors that constrain the behavior and define the nature of doctoral students' academic role identities. This multiple case study used open-ended reflective questions and narrative-style interviews with eight physical science doctoral students to explore how physical science doctoral students navigate their role identities throughout their graduate programme and the factors that may influence these identities. Responses to the reflective questions and narrative interview transcripts were qualitatively coded and salient themes are drawn through cross-case analysis. Themes were compared across data sources to further validate the findings. Participants ascribed the most value to researcher and student identities and the least value to an educator identity. Time spent in a role, institutional recognition, advisor relationships, community in graduate school, and interest were factors that participants perceived to influence their role identities, along with the gender identity of women. Implications highlight the ways in which institutions may be able to support doctoral students in graduate school, including increased support for time management, equitable opportunities for authentic research experiences, equitable support in advisor relationships, and the importance of intentionally fostering community within science departments.