<P> The Rat Pack is a term used by the media to refer to an informal group of entertainers centered on the Las Vegas casino scene . Having its origins in a group of friends that met at the Los Angeles home of Humphrey Bogart and Lauren Bacall, by the 1960s, it was the name used by the press and the general public to refer to a later variation of the group that called itself "the Summit" or "the Clan", featuring Frank Sinatra, Dean Martin, Sammy Davis Jr., Peter Lawford and Joey Bishop among others; they appeared together on stage and in films in the early 1960s, including the movies Ocean's 11, Sergeants 3, and Robin and the 7 Hoods (in the last film, Bing Crosby replaced Lawford). Sinatra, Martin, and Davis were regarded as the group's lead members . </P> <P> The name "The Rat Pack" was first used to refer to a group of friends in New York . Several explanations have been offered for the famous name over the years . According to one version, the group's original "Den Mother", Lauren Bacall, after seeing her husband, Humphrey Bogart, and his friends return from a night in Las Vegas, said words to the effect of "You look like a goddamn rat pack ." "Rat Pack" may also be a shortened version of "Holmby Hills Rat Pack", a reference to the home of Bogart and Bacall which served as a regular hangout . </P>

Who was the fourth member of the rat pack
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