The Rat Pack was the name given to a few choice friends of Frank Sinatra who performed and caroused with him in the early 1960s.
The Rat Pack was never an official title -- the name is said to have been borrowed from a group of drinking buddies of Humphrey Bogart who were dubbed a "rat pack" by Bogart's wife Lauren Bacall. But the name stuck to Sinatra's gang, and nostalgia for the Rat Pack only seems to increase as time goes by.
The Pack's high-water mark came in 1960, when the group hit Las Vegas to make the spoofy heist film Ocean's Eleven. Sinatra and chums filmed during the day, did two live shows nightly at The Sands, and drew crowds and publicity wherever they went.