The Other Darrin: There were no less than three different voice actors for Arthur. And it was very noticeable. Two sound very similar: young and squeaky. While the other is the voice of a teenager who's gone through puberty.
Two of which sound a lot like Mowgli or Christopher Robin. While neither of them voiced Mowgli or Christopher Robin, the older one did. Two of them are also animator/director Wolfgang Reitherman's sons.