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?