In addition to developing innovative research programs, life science research faculty at research-intensive institutions are tasked with providing career mentoring and scientific training to new generations of scientists, including postgraduate, graduate, and undergraduate students. In this essay, we argue for a redefinition of mentoring in laboratory research, to thoroughly distinguish three essential roles played by research faculty relative to their trainees: advisor, educator, and supervisor. In particular, we pay attention to the often unacknowledged and misunderstood role of a faculty member as a supervisor and discuss the impact of neglecting supervisory best practices on trainees, on the diversity of the academic pipeline, and on the research enterprise. We also provide actionable frameworks for research mentors who wish to use inclusive supervisory and pedagogical practices in their laboratory. Finally, we call for more research around the supervisory role of research faculty and its impact on trainees, particularly community college students, in order to help broaden the participation of underrepresented students in STEM fields.