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".

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.

After two years with Ripley, Clarke joined the army, where he worked for the European edition of Stars and Stripes and met his wife.

Clarke remained with Stars and Stripes after being discharged as a civilian contributor, before eventually returning to America and joining the advertising firm Geyer, Newell, and Ganger.

Clarke was a mainstay of the magazine as it rose in circulation, being one of four general-purpose artists who took MAD through the late 1950s and earliest 1960s, the others being Wallace Wood, George Woodbridge and Joe Orlando (Jack Rickard's work appeared in mid-1961, while Don Martin, Mort Drucker and Dave Berg produced more specialized topics or features).

His most revealing pose was for a 1989 MAD Special for which he'd been assigned to create an actual pair of men's boxer shorts with a repeating pattern of Alfred E. Neuman's face.