This paper discusses one of the fundamental issues in education and social program evaluation: the proper role for an evaluator. Based on respective and comparative analysis of five theorists' positions on this fundamental issue, this paper reveals how different perspectives on other fundamental issues in evaluation such as value, methods, use and purposes can result in different roles for evaluators, and how such difference can affect evaluators' responsibilities in different stages of an evaluation. Then the paper proposes its own resolution of the issue of evaluator's role and discusses its implication and limitations.