Harvey Muckenthaler is the main antagonist of some Stuart sketches. He is Stuart's arch-nemesis and next door neighbor.

The reason Harvey cannot stand Stuart is because he always annoys and disobeys him.

Doreen appears to have somewhat of a crush on him (as she tends to flirt with him when Stuart is not around) until the end of "Moving Day," in which Doreen kicks Harvey out of her house for revealing his true feelings for Stuart and Doreen and insulting them by calling them freaks. This soon drives them to exact revenge by not moving after all.

In "Moving Day," Stuart claims that Harvey is clearly borderline homosexual. However, he could have been thinking that since Harvey was whispering to his friends during poker, Stuart could have assumed that Harvey was (as Doreen says about people who whisper) either sneaky or homosexual.

He is portrayed by Paul Vogt.