Family Guy has the two vaudeville performers Vern (skinny) and Johnny (fat). Expy counterparts from the other, time Bokan series. Depending on the artist or screen portrayal, Sherlock Holmes and John Watson sometimes get this treatment.
To explain, Rob is basically Hollywood Pudgy and has had his own moments of scary-thin. Tennessee Tuxedo and Chumley from Tennessee Tuxedo And His Tales.