Doctor Augustus P. Crumhorn recurred as Danger Mouse's adversary less frequently than Baron Greenback. In one episode, he attempted to undermine Danger Mouse by metamorphosing into a Shirley Temple lookalike. In only one episode, "Penfold Transformed", he lists his full name as, "Aloisius Julian Philibert Elphinstone Eugene Dionysis Barry Manilow Crumhorn", omitting both Augustus and the III. Crumhorn was rarely if ever seen among American audiences, who had to purchase the original version aired on ITV to experience his ridiculousness. Crumhorn and Greenback were at odds; once Crumhorn kidnapped Penfold and Penfold managed to escape simply because, the two villains were too busy quarreling to notice his absence.

In the reboot series episode Mousefall, Crumhorn is revealed to be the father of Augustus Crumhorn IV and grandfather of child villain The Princess (real name Dawn).