Humphrey Carpenter got it wrong. This painting was painted after Tolkien had written The Hobbit.
There are of course several possibilities:
- Tolkien didn’t know where he’d got the idea for Gandalf from.
- Tolkien knew about Rübezahl ‘mit seinen zwergen’ before this picture was painted.
- Rübezahl is currently depicted as more Gandalf-like (he now has a broad-brimmed hat, a long staff and, most improbably of all, a long pipe) to make him more tourist friendly.
Personally I find 2. most appealing. Carpenter is only one amongst many Tolkien biographers/"scholars" who has pushed the idea of Tolkien the geek, Tolkien the nerd, perhaps even Tolkien the philistine, who knew precious little of the world, much less of culture and art generally, outside of his own narrow academic field.
In actual fact, though there is no direct evidence that Tolkien knew about Rübezahl, there are various details about him that make him a good model for Gandalf.
He’s a mountain giant. (There are mountain giant, or “rock giants”, mentioned in
The Hobbit - by Gandalf - and, very unusually for Tolkien’s creations, there’s not so much as a corroborative mention of them anywhere else.)
He has “dwarfs” with him.
He has more than one name.
He’s a liminal being - specifically one who ranges the mountains between modern Poland and the Czech Republic (traditionally Silesia and the Bohemian Sudetenland) and hence, in Tolkienian fashion, his various names.
Most poignantly of all, since
The Hobbit’s publication, the German-speaking people of Rübezahl’s realm have themselves become exiles, having been driven westward in the anti-German campaign of ethnic cleansing that followed WWII.
(Personally I have a strong suspicion that since his death Tolkien’s political views have been significantly censored, if not actually bowdlerized - so we’re allowed to know that he was a Tory, a monarchist, proto-libertarian (though he preferred to think of himself as a "philosophical" anarchist), something of a philo-Semite (and staunch, though not necessarily outspoken anti-Nazi), a firm patriot, a bit of a “greenie”, and something of a Luddite, and that he found the changes to the Mass post-Vatican II deeply hurtful. But what he really thought about de-colonialisation, mass non-white immigration, Britain’s entry into the European common market, or even about wars in Suez, Korea or Vietnam, we simply do not know - although it’s quite possible that since he didn’t read newspapers he wouldn’t have felt qualified to venture opinions on many of these things.)