Truman (played by Michael Ontkean) is Twin Peaks' sheriff who assists Special Agent Dale Cooper in the investigation of the murder of Laura Palmer. Harry is in love with fragile Josie Packard, and he is one of the Bookhouse Boys.

Harry gets on well with Cooper. They hit it off almost from the start. Harry is very down-to-earth in contrast with Cooper's unconventional methods of policing, fascination with Tibet, dreams, etc. Harry regards Cooper as somewhat eccentric but well-meaning. In early episodes, Harry serves to introduce Cooper (and hence the viewer) to the more prominent residents of Twin Peaks. Harry begins to feel that he is the Dr. Watson to Cooper's Sherlock Holmes. Despite their differences, Truman represents a literary alternate to Cooper: they approach the same goal through different means.

As the case progress, Harry's respect for Cooper grows. He regards Coop as "the finest lawman he has ever known".