Grant is a member of a project team. His colleagues in the team rely on him to read and check complex project documentation. Grant has a keen eye for detail and often identifies minor details in documents that others miss but may be of significance. Despite the diligent approach, Grant always meets his deadlines. However, some of Grant's colleagues feel frustrated when he refuses to involve others. He can hold up progress as he will not agree to the team signing off project documents until all of his concerns are fully discussed.According to Belbin's team roles theory, Grant is an example of which of the following?