It was almost 40 years ago that the USPS, in an ad for its Stamps and Stories book, a sort of mini catalog of all the U.S. stamp issues, asked rhetorically "What does it take to get on a stamp?"
Among the entertaining answers were "Never meet a man you don't like." (Will Rogers); "Be the father of a mouse." (Walt Disney); and "Take a stroll on the moon." (Neal Armstrong, unnamed due to the rule of the living not appearing on U.S. stamps, although the astronaut pictured could only be Neal Armstrong.)
But one thing is still necessary to appear on a U.S. stamp, now that the USPS has pulled back from its plan of issuing stamps featuring living people: dying.