Not knowing the history of this particular star
name, isn't it also possible that Charlemagne was associated with the
constellation by folk etymology? If the constellation was originally called "the
churl's wain" (*karla-wagnen, "the peasant's waggon"), this name might easily be
confused with Latin Carolus Magnus (especially wagn- vs. magn-), especially
since Latin Carolus is simply a Latinized Germanic Karl.
-C. Gwinn