"Feldstein's successor John Ficarra said of Clarke, "He was a great designer, and he also was a terrific mimic of other people’s styles... And if there was a problem you could give it to Bob, and he could usually solve it for you.”

Clarke's earliest professional job was at the age of 17, as an uncredited assistant on the "Ripley's Believe It or Not" comic strip.Ripley traveled the world collecting his fantastic trivia tidbits and sent them back to Clarke who drew them, captioned them and circulated them among the vast number of magazines and newspapers who carried the strip.