According to Gil Fates in his What's My Line? memoir, the idea for a show called I've Got A Secret was brought to Goodson-Todman by comedy writer Allan Sherman and his partner, Howard Merrill.  The producers, of course, recognized it as a simple variation on their What's My Line? and told the young pair they didn't want to rip off their own successful program.  "You might as well," Sherman said, "because if you don't start copying your shows, someone else will."  Goodson and Todman agreed, paid both men a royalty and named Sherman associate producer of the new venture.  Years later, Sherman would make a name for himself with a series of novelty folk songs including Hello Mudda, Hello Fadda.

Popular Garry Moore was chosen to host the show.  There was a great deal of turnover on the panel in the first year of the series, perhaps as the producers worked to find the proper chemistry.  None of the original panelists (actress Louise Albritton, comic actor Orson Bean, Broadway vet Melville Cooper and author Laura Hobson) stayed with the show past the first thirteen weeks.  Bill and Jayne Meadows (later to become Mrs. Steve Allen) replaced Albritton and Bean and quickly became regulars.  Original panelist Cooper was replaced by comic Eddie Bracken on October 9.  Bracken appeared in six shows before being replaced by Henry Morgan on November 13.  Morgan stayed with the show thereafter, his cranky and sarcastic demeanor a perfect counterpoint to Bill's boyish enthusiasm.  The second female chair was filled for weeks at a time by several "bright young actresses", including Larraine Day (Mrs. Leo Durocher), Nina Foch and Kitty Carlisle.  By early 1953, Faye Emerson had emerged as the fourth regular.
 

The team of Cullen, Meadows, Morgan and Emerson remained intact for several years, affected only when one of the ladies took acting jobs that interfered.  That became more common as roles became more available in California than in New York.   Stage actress Betsy Palmer began appearing on the panel in 1957.  New York personality and former Miss America Bess Myerson joined in 1958.  Soon, the new regular line-up became Cullen, Palmer, Morgan and Myerson, and it remained that way through the run of the series.  (Meadows and Emerson had become west coast residents, but still visited the show on occasion.)

The final four-member panel was about as perfect as this sort of thing can be.  Funny Bill, spunky Betsy, grumpy Henry and glamorous Bess brought diverse backgrounds and styles to the game.  They seemed a family to TV viewers, although like most panels, they seldom even socialized off-camera.  (Bill once said of Palmer, "I never got to know her until she'd been showing up regularly for three or four months.")  It was even easy to pair them off, Bill and Betsy representing youthful exuberance, Henry and Bess suggesting worldly (in Morgan's case, world-weary) sophistication.  Not surprisingly, that's the way they were usually paired when a game required it.

With the panel relatively stable, the guest stars provided variety.  Visiting celebrities brought a lot more entertainment to the show than did the What's My Line? mystery guests.  For one thing, their appearance could be promoted, since it was not supposed to be hidden from the panel.  Also, as the years went on, the idea of having a celebrity "secret" for the panel to guess became less and less important, and the guest stars would often introduce some entirely different parlor game to play instead.  Even many of the traditional contestants had some sort of musical or other performance-related secret, which would inevitably be demonstrated after the questioning was through.  It no longer remotely mattered whether the panel got one right, again unlike What's My Line?, which took its game seriously until the end.  I've Got A Secret became a variety show masquerading as a game show.
 

Bill described the cushy Secret job in a 1967 interview.  "It's been like stealing," he said.  "Imagine getting paid handsomely to turn up at a studio every other week at 7pm in a clean shirt, without preparation, and play a parlor game for a half-hour.  Then there was time to smoke a cigarette and maybe talk to Henry Morgan awhile, and then play a parlor game for another half hour and go home."

As the loosest of all the panel shows, as well as the highest-rated, I've Got A Secret was probably more influential than even What's My Line?, its older sibling.  An entire generation of Nickelodeon watchers, for example, have no idea how much the popular Figure It Out resembles Secret.

VIDEO         
The vast majority of episodes have survived, though not the first few.  Most of these episodes have turned up on GSN, including a great number of episodes which were originally sponsored by Winston cigarettes.  GSN has aired classic episodes of I've Got A Secret as recently as December, 2009 as part of their Black and White Overnight block of shows, though it is not on their current schedule.

Watch an early episode with Lucille Ball and some great secrets:

 

Watch a 1967 episode with Pearl Bailey:

FOR MORE INFORMATION       
Tommy Gun's I've Got A Secret Online is an amazing repository of information, including a detailed episode guiide.
Adam Nedeff's classic I've Got A Secret page at Bill Cullen's World
The I've Got A Secret page on Wikipedia

Bill hosted this four-week summer replacement series, with Henry Morgan returning as a regular panelist.