I always thought so though listening last night to radio 2 they said the official website claims he is a mole!!! Blatant specieism, what's wrong with being a hamster anyway well apart from being used by sexual deviants.
Not sure of the official website, but http://www.dangermouse.org
says he was a hamster as well. In fact I've only found 2 references to him being a mole, both comments in guestbooks rather than in official site material.
OK folks end of argument. Mark Hall (of Cosgrove Hall, who invented Dangermouse) says that originally Penfold was going to be a worm, but eventually became... a HAMSTER. Now, if the inventor of Dangermouse says Penfold's a hamster, he's a hamster, no matter what else he may happen to look like. The reference for this is http://www.classictelevision.info/cartoons04.htm
if you want to check it. Everybody clear now?
It's OK Tj - I've slept on it, and I have now come to terms with it - yes, Penfold is a hamster (albeit a very strange-looking one) - all the written evidence points to that fact, so it can't be disputed. But I will always think of him as a mole! As for Colonel K? Who knows? Cosgrove Hall aren't sure - probably a gopher. But he doesn't look much like Gordon the Gopher does he??!! Whatever happened to him? :-)