There are opinion leaders in a society who represent the opinion of general public. The general public accepts information not only by mass media but also by opinion leaders. Since the late 20th century, the number of Internet users has increased fast. Many users interact with each other in an online social network. This makes the Web community similar to the real society. Thus it is a natural task to find influential users in an online society. For example, many online articles posted by influential bloggers are used as marketing tools for companies or political advertisements for parties since these articles have huge influence to other users. We first revisit the previous researches on finding influential users in online society. Then we compose test sets from GroupLens movie database and identify representative reviewers. Next, we show the validity of the chosen representative reviewers and test the reliability using the 10-fold cross-validation. Finally, we explain applicability of the proposed approach to improve current recommendation systems.