Keith just said this could be his last show?

In late 1950s America, a time during which television was rapidly replacing radio as the most popular entertainment medium, Larry "Lonesome" Rhodes, while coarse and abusive in private, possesses a charm that quickly endears him to rural listeners after Marcia Jeffries (Neal), a small-town radio personality, discovers him in the county jail of the fictional town of Pickett in northeast Arkansas and lands him a radio show.

A talent scout invites him to appear on television in Memphis, Tennessee, where Rhodes is introduced to Mel Miller (Matthau), a bookish Vanderbilt University graduate who writes his scripts. Rhodes makes a name for himself by insulting his sponsor — to the delight of his adoring audience. Rhodes's sponsor, whose company sells mattresses, relents in canceling the show when he discovers that Rhodes's antics increased sales by 55%.

An opportunistic "office boy" (portrayed by Anthony Franciosa) acts as an agent and lands Rhodes a contract in New York City, where he stars in his own national television program and becomes the national TV spokesman for Vitajex, an innocuous dietary supplement. A frenetic montage of Rhodes's hyperbolic ads for Vitajex, suggesting it has Viagra-like powers, is one of the film's most memorable sequences, highlighting the presumed gullibility of the American public to a persuasive con-artist.

Rhodes' fame, influence and ego grow. He is called in as an adviser by national political campaigns, rudely instructing candidates how to gain the public's trust and suggesting himself for a Cabinet-level post. Rhodes uses his TV program to give exposure to his presidential candidate of choice, while mocking the man in private to his various sycophants.