Oh, dear. How do you even start explaining a German 60s (yes, I know it went on up until at least the 90s, but I more or less learned to read on my dad's weekly fix) cult science fiction pulp series to a bunch of brits and americans without sounding weird? Even here?
Google "Mausbiber Gucky". Mouse-beaver would be a translation of "Mausbiber". Some people would call him a large rat, but most who did that spent the rest of the day pinned to a ceiling somewhere.
Found an image of him from one of the early original covers on
perrypedia:
To the OP: wrong franchise. Copyright law is a female dog. You'll get Gucky probably soon after the Wookie, possibly slightly before Barf and immediately after hell freezes over. Not sure about Rocket, though.