This is addressed here:
Dear Mr. Adams:
I notice that Dilbert and Dogbert look like Sherman and Peabody, the old Saturday morning cartoon. Is that a coincidence?
It's not a coincidence. Mr. Adams' original concept for Dilbert was a British guy who was a wife-beating, alcoholic, unemployed adulterer. I played the part of the wife who waited for him at night with a rolling pin. But when Mr. Adams submitted this idea to United Media they informed him that it had "already been done."
Fortunately, United Media recognized a spark of creative genius in Mr. Adams. Their editorial staff worked with him to do something that nobody had done before: rip off Sherman and Peabody. You're the first person to notice.