DC introduced SHOWCASE in March 1956. The page shown below, from Showcase #1, explains DC's reasons for creating the new title:
BELOW: AN Ira Schnapp-designed in-house ad for SHOWCASE #1:
In the 1960s, the huge popularity of the James Bond movies and The Man from U.N.C.L.E. TV series led readers to ask DC for a secret agent hero, so Showcase editor Lawrence Nadle created a spy who was a master of disguise, slated to debut in Showcase #50, naming him YANKEE DOODLE DANDY. Unfortunately, Nadle passed away before the story was begun, leaving the character with only a logo (probably by Ira Schnapp), and a cover (seen below). Comics.org says it was drawn by Mike Sekowsky and Frank Giacoia -- but Mike Tiefenbacher has identified the penciller as Bob Oksner, who was working with Nadle at this time. Robby is convinced it's true! Take a look at the ear on the man in the lower right corner. That's an Oksner ear!
Following Nadle's sudden passing, the YANKEE DOODLE DANDY cover and character were shelved, and replaced by reprints starring a secret agent named King Faraday under the updated and "modernized" title "I--Spy!"
The original cover art for YANKEE DOODLE DANDY was rediscovered in 1992, and resurrected for use on DOOM PATROL #51, which featured a wild new version of the character created by Grant Morrison, Richard Case and Stan Woch.
The last page of DP #51 revealed the freakish new John Dandy:
THIS CONTEST IS NOW OVER!
Winner and runners-up pictured below!