Before Frank Sinatra assembled his Las Vegas Rat Pack of the 60's, he was part of an earlier Rat Pack group of the 50's set in Holmby Hills California, near Beverly Hills. It centered around Humphrey Bogart and his wife Lauren Bacall, who is believed to have come up with the name, not necessarily as a compliment.
There were even titles for the key members, with Bogart as rat in charge of public relations, Bacall as den mother, Judy Garland as first vice-president, her husband Sid Luft as cage master, and agent Swifty Lazar as recording secretary and treasurer, plus of course, Frank Sinatra as pack master.
Other members of the original Rat Pack were actors David Niven, Katharine Hepburn, and Spencer Tracy, director George Cukor, restaurateur Michael Romanoff, and Sinatra friend and songwriter Jimmy Van Heusen.
Someone in the group even created a coat of arms -- a rat gnawing on a human hand, and a motto: "Never rat on a rat". But in spite of those refinements, and those official titles, the members' only real responsibilities were to show up and drink together.
Today, it's Frank's 60's group that's re-created in theaters and casinos presenting tributes to the Rat Pack, featuring performers known as Rat Pack Impersonators.