I did find one possibility online in a review of Zachary Wheeler’s _Max and the Multiverse_ (described as a “a young adult science fiction novel”) :

   I hope Max makes it farther in the galaxy than Walter Dent
    ever dared to explore!

   < http://www.larc-scifi.com/MaxandtheMultiverse.html >

Anyone recognize this?

--Voragh

From: nIqolay Q

On Fri, Oct 20, 2017 at 1:32 PM, kechpaja <kechpaja@comcast.net> wrote:

So is there a famous Walter Dent out there who I should have heard of?
Or is there another pun I'm missing?

I had the same thought when the word got released, but so far I haven't found any Walter Dents who seem famous enough to be a reference. It might just be someone Okrand knows personally. (Or it's something else entirely and it's only coincidence that it looks like "walter" backwards.)