The Rat Pack was a group of actors originally centered on Humphrey Bogart.
In the mid-1960s, it was the name used by the press and the general public to refer to a later variation of the group, after Bogart's death, featuring Frank Sinatra, Dean Martin, Sammy Davis, Jr., Peter Lawford, and Joey Bishop... who appeared together on stage and in films in the early 1960s.
Sinatra, Martin, and Davis were regarded as the group's lead members.