Undergraduate research has been documented as yielding valuable student learning outcomes. While the outcomes have been extensively investigated, the development and characteristics of the relationship with the research mentor has received less attention. To better understand how participating in undergraduate research yields substantial benefits to students, we need to elucidate the relationship between students and their research mentors. Using survey and focus group data from a select group of undergraduate researchers at one research university, we investigated the origins of undergraduate research mentoring relationships, the development of those relationships over time, and how the characteristics of the mentoring relationship yielded a shift in identity among the undergraduates. In this case study we found that the meaningful relationships developed between students and their mentors contributed to student development in the form of increased confidence and perceived competency. This competency led to changed expectations of self in the professional sphere, a deeper sense of belonging, and changed expectations for post-graduation.