This study addresses a gap in Translation and Interpreting (T&I) research by examining interpreter trainers’ beliefs and identities, which play a crucial role in shaping learning outcomes. Focusing on part-time interpreter trainers who also work as professional interpreters, the study explores the trainers’ conceptualizations of interpreting quality, interpreter competencies, interpreter training, and their identities as educators. Five interpreter trainers were recruited from a graduate school of interpretation and translation in Seoul, Korea, including three junior trainers with under three years of teaching experience and two senior trainers with over ten years. In-depth, semi-structured interviews examined participants’ motivations for teaching, perspectives on quality interpreting, the relationship between teaching and practice, and self-concepts as trainers. The study showed that the participants found teaching rewarding, viewing it as complementary to professional practice. Junior trainers, however, expressed challenges in providing feedback and assessment; they see themselves as learning facilitators, focused on supporting students in developing interpreting competencies. Senior trainers view their roles as mentors, offering guidance as experienced professionals. Based on these insights, the study suggests pedagogical strategies to improve interpreter training programs.