Harold is a former professor who died prior to "Coming Out of the Casket" and comes back to life as a ghost. Both before his death and during his reincarnation, it's shown that he's popular around the campus.
Harold returns to life with the intent of telling Frank something, but it remains unknown for a while. When Harold makes this known by kissing Frank, he subsequently comes out of the closet, under the impression that Frank is as well. Suddenly, Harold is captured by the Spanish department and placed in his corpse to curb the history department's popularity. During his entrapment, Harold sends Frank an apology text for the assumption, and when Frank reads it aloud, the crowd returns to the history department, making it popular again. Still in his corpse, Harold asks for the plug to be pulled, and his spirit leaves the corpse.