From the U.S. Postal Service website (about.usps.com):
The cartoon figure, Mr. ZIP, was adopted by the Postal Service as the trademark for the Zoning Improvement Plan or ZIP Code, which began on July 1, 1963. However, the figure originated several years earlier. It was designed ... for use by Chase Manhattan Bank in New York in a bank-by-mail campaign. ... The figure was used only a few times, then filed away. The American Telephone and Telegraph Company acquired the design and made it available to the Post Office Department without cost. The new figure, dubbed Mr. ZIP, was unveiled by the Post Office Department at a convention of postmasters in October 1962.
* "Mr. Zip and the ZIP Code Promotional Campaign" (from National Postal Museum): @
* "U.S. to ZIP mail through" (Scripps-Howard article, November 1962): @