How many characters are played by multiple actors on Bob's sitcoms?

In my Q&A with Dave Coulier (see previous post), we discussed the change of actresses in GEORGE & LEO's "Casey" role. And that got me wondering: What other characters from Bob's four major sitcoms -- THE BOB NEWHART SHOW, NEWHART, BOB or GEORGE & LEO -- were portrayed by multiple actors?

Off the top of my head, I remember that Arthur Vanderkellen (Stephanie's father) on NEWHART was played by one actor (who turns out to be one Richard Roat, an actor with whom I'm not familiar) only to be replaced by the famous thespian Jose Ferrer when the millionaire part became a recurring character. Insofar as I know, Roat only played him in that one appearance, the episode "It Happened One Afternoon Part 2."

Any other characters portrayed by multiple actors? Let me know! --Mike Malloy