The Purple Cow is Williams' mascot, after the infamous poem by Gelett Burgess:
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.
This was later followed by a sequel:
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.
The Purple Cow is also the name of Williams' first humor magazine.