Robert Day was a long-time contributor to the New Yorker while also contributing spot illustrations to Reader's Digest. He died shortly before Charles Addams; the New Yorker promptly gave Day a long detailed obituary but was much slower in honoring Addams.
Day's cartoons were prized by editors; whereas another cartoonist might attach a funny caption to a fairly routine drawing of two people talking, Day's cartoons were usually funny in themselves even with a caption.
He often created extremely elaborate drawings. A typical Day cartoon showed a mushroom soup factory, with thousands of mushrooms sliding down chutes into enormous vats. On a gantry high overhead, a supervisor shouts: "Hold everything! There goes a toadstool!"
One of Day's most famous cartoons depicted dozens of birds roosting on an offshore rock. The tour guide on a passing boat announces "We are now passing Bird Rock". Allegedly, after this cartoon was published, cartoonists and their editors began using the term "a Bird Rock" to identify any cartoon that merely illustrated its own caption.