Answer
Frank Sinatra was a famous Rat Pack friend of Rickles. The Rat Pack was a group of American entertainers who were active from the late 1950s to the early 1960s. The group included Sinatra, Sammy Davis Jr., Dean Martin, Peter Lawford, and Joey Bishop. The Rat Pack was known for their wild parties and their close friendship. Rickles was a close friend of Sinatra and the two often performed together.