In 1985, American newspaper readers met an appalling little boy. He taunted his mother (“Prepare for annihilation, pitiful Earth female”), tormented a classmate by telling her he had brought a “thermos full of phlegm” for lunch and kept a sign on his bedroom door that read “Enter and die.” Millions fell in love with him.

Running in hundreds of papers for the following decade, Bill Watterson’s “Calvin and Hobbes” was not only the strangest American comic strip. It was also the funniest, the most touching and the most profound....