Dan Harmon is best known as the creator of the comedy show movie.
Over the course of the show, Community had a wide and impressive variety of guest stars, with celebrities featuring as everything from minor, one-off characters, to comedically warped versions of themselves. The cameos that best reflected the show's meta-humor, however, were those of Dan Harmon himself. Although Harmon did not have a physical cameo in the show, he provided his voice for characters on three separate occasions.
Harmon's first cameo was in the season 3 episode, "Curriculum Unavailable," in which he voices an alternate version of the recurring character, Garrett. After being expelled from Greendale, the study group is forced to see a psychiatrist, who, unbeknownst to them, is actually an actor hired by One of Community's animated episodes, "G.I Jeff" is done partially in the style of the 1980s G.I. Joe cartoons, and Sleep Apnea is a perfect cartoon Harmon.
Harmon's third voice appearance was in the series finale, "Emotional Consequences of Broadcast Television." In the show's last end tag, the series parodies the merchandising of franchises with a fake ment for a Community board game. The ment starts out as stereotypical and predictable but quickly becomes a meta-commentary on the show and its self-aware nature. Harmon, as the commercial announcer, drives this commentary and makes references to his tumultuous relationship with NBC, the dedicated fanbase, and the changes the show went through over the years. Unlike with his previous cameos, Harmon makes his presence known, ranting about his status as the Community's creator and changing roles over the seasons. The scene is a perfect way to end the show, and it's fitting that Harmon is the last voice ever heard on Community.
With creative storytelling, referential humor, and unique spins on classic tropes, Community was able to become an essential contribution to the sitcom canon, with no small thanks to Dan Harmon. With his voice cameos, Harmon was able to further leave his mark on Community and showcase the various forms that the series could take on. Although he never physically appeared in the show, Harmon's cameos were all iconic in their own ways and helped to make the episodes all the more memorable.