A colleague of Hetherington's pointed out that his paper used the royal "we" throughout the paper. Physical Review Letters only used the word "we" as a plural pronoun, indicating multiple people. Hetherington put in all this work, and couldn't simply replace it so easily, since this was 1975 and it was all written out on a typewriter.
Hetherington was willing to share credit with his Siamese cat, Chester. To make it a bit more official, he came up with the name F.D.C. Willard. The meaning behind the name is "Felix Domesticus Chester," and Willard was the name of Chester's father.
Hetherington portrayed F.D.C. Willard as one of his MSU colleagues. He turned in the paper, and it was published in issue 35 of Physical Review Letters. It didn't take long for folks to figure out that F.D.C. was a cat, especially when they looked at his signature.
"Why would I do such an irreverent thing? … If it eventually proved to be correct, people would remember the paper more if the anomalous authorship were known. In any case I went ahead and did it and have generally not been sorry."
Once Chester/Willard's identity was revealed, Hetherington kept the joke going. He began describing his "colleague" as their university's "Rodentia Predation Consultant." But how did the university react?
They loved it. The college’s Physics Chairman, Truman Woodruff, even wrote a letter asking if Hetherington could convince Willard to join the department full time. Or, at the very least, as a "Visiting Distinguished Professor."
Willard's works have had lasting repercussions. In 2014, the American Physical Society announced any paper written by a feline would be an open-access document. Before getting too excited, you should know this announcement was made on April 1st.