I had forgotten about F.D.C. Willard.
Some years back, I referred to him in a class on critical appraisal, as a way into the idea that journal articles are not always what they seem.
I was reminded, and delighted to be so, by The Scholarly Web column in today's THE (6-12 August 2015, p. 21), which was talking about the Academia Obscura blog, which mentions it.
So, this is the story. This paper in Physical Review Letters, in low temperature physics, was written by J.H. Hetherington. A colleague of Hetherington's pointed out that the journal's rules said that if there was one author, you could not say "we" did this or "we" found that, but you must write "I". To avoid this, Hetherington (a real physicist and author of 40 papers indexed in Web of Science) added his cat, F.D.C. Willard as co-author. The cat was called Chester, his father (the cat's) was Willard, and F.D. is (I used to ask the students if they could guess) for Felis domesticus.
This paper has been cited 59 times in Web of Science,
The story is recounted in:
Nickon A, Silversmith E.F. Organic chemistry: the name game. Modern coined terms and their origin. Elsevier, 2013
Stall S. 100 cats who changed civilization: history's most influential felines. Quirk, 2011
Weber RL. More random walks in science. CRC Press, 1982. (A Google search turns up a book in German, called Kammerphysikalische Kostbarkeiten, which turns out to be a translation of this). This, I think, is the book where I found the story.
The relevant sections are all in Google Books. There is also an article in Wikipedia that tells the story, with a few developments I did not know about, and some references (although some are broken links).
And (added the day after I wrote the original post, and causing some amendments), Hetherington's account of it is in this article from Physics Today from 1997 (you will need a subscription or payment to read the whole article).