I Never Saw a Purple Cow
Written by Frank Gelett Burgess in 1895

I never saw a purple cow,
I never hope to see one;
But I can tell you, anyhow,
I'd rather see than be one.

Then, in 1914 Frank Gelett Burgess wrote...

Ah yes, I wrote the "Purple Cow"--
I'm sorry now, I wrote it!
But I can tell you, anyhow,
I'll kill you if you quote it.