The mentor plays an important role in initiating a process of cumulative advantage for the student. Our analyses present a clear and systematic pattern of effects of the mentor on the careers of biochemists. The influence of the mentor begins with collaboration, which is the single most important factor affecting the student's predoctoral productivity. For those who collaborate, the effects of both eminence and performance further increase the student's predoctoral productivity. The mentor's performance has weak effects on the productivity of noncollaborating students. For those who collaborate with their mentor, the mentor continues to influence the career with a positive effect of the mentor's performance on academic placement, an effect not found for noncollaborators. Even though the mentor's performance affects the student's placement, the student's performances doesnot affect that placement, suggesting a process of ascription. For those who collaborate with their mentor, the mentor's performance increases the student's later publications and citations. For noncollaborators, whose mentors are much less productive during the student's period of doctoral study, the mentor's eminence has a smaller, but significant effect on later productivity. Overall, the advantages of a strong mentor are drawn upon and enhanced through processes of both achievement and ascription.