Karloff and Diller's characters are both designed to look like the actors portraying them, while Baron Frankenstein's lackey, Yetch, is a physical and vocal caricature of Peter Lorre. Swift also performs impersonations when voicing his characters, such as James Stewart when voicing Felix, Sydney Greenstreet as the Invisible Man and Charles Laughton as the Freighter Captain.
Karloff and Diller's characters are based on their actors, while Yetch, a servant of Baron Frankenstein, is a caricature of Peter Lorre.  Additionally, voice actor Swift impersonates various characters, including James Stewart as Felix, Sydney Greenstreet as the Invisible Man, and Charles Laughton as the Freighter Captain.