The Ruling Class is a 1972 British black comedy film. It is an adaptation of Peter Barnes' satirical 1968 stage play The Ruling Class, which tells the story of a paranoid schizophrenic British nobleman (played by Peter O'Toole) who inherits a peerage. The film co-stars Alastair Sim, William Mervyn, Coral Browne, Harry Andrews, Carolyn Seymour, James Villiers and Arthur Lowe. It was produced by Jules Buck and directed by Peter Medak.

The film has been described as a "commercial failure ... [that] has since become a cult classic"; Peter O'Toole described it as "a comedy with tragic relief".

Following the death from accidental asphyxiation of Ralph Gurney, 13th Earl of Gurney, Jack Gurney becomes the 14th Earl of Gurney. Jack, a paranoid schizophrenic, thinks he is Jesus Christ and shocks his family and friends with his talk of returning to the world to bring it love and charity, not to mention his penchant for breaking out into song and dance routines and sleeping upright on a cross. When faced with unpalatable facts (such as his identity as the 14th Earl), Jack puts them in his "galvanized pressure cooker" and they disappear. His unscrupulous uncle, Sir Charles, marries him to his mistress, Grace, in hopes of producing an heir and putting his nephew in an institution; the plan fails, however, when Grace falls in love with Jack. Jack gains another ally in Sir Charles' wife, Lady Claire, who hates her husband and befriends Jack just to spite him. She also begins sleeping with Jack's psychiatrist, Dr. Herder, to persuade him to cure Jack quickly.

Herder attempts to cure him through intensive psychotherapy, to no avail; Jack so thoroughly believes that he is the "God of Love" that he dismisses any suggestion to the contrary as insane. The night his wife goes into labour, Herder makes a last effort at curing Jack; he introduces Jack to McKyle, a patient who also believes himself to be Christ – or as the patient puts it, "The High Voltage Messiah" – who subjects an unwitting Jack to electroshock therapy. The plan works, and as Grace is delivered of a healthy baby boy, Jack proclaims "I'm Jack, I'm Jack". His family takes this to mean that he has returned to his senses, but in reality he now believes himself to be Jack the Ripper.

Sir Charles sends for a court-appointed psychiatrist to evaluate Jack, confident that his nephew will be sent to an asylum for life. He is once again thwarted when the psychiatrist discovers that Jack was a fellow Old Etonian, bonds with him and declares him sane.

Jack murders Lady Claire in a fit of rage when the ageing woman tries to seduce him. He frames the Communist family butler, Tucker, for the murder. Sir Charles suffers a debilitating stroke shortly afterward, and Dr. Herder has a nervous breakdown upon realizing what Jack has done. Jack assumes his place in the House of Lords with a fiery speech in favour of capital and corporal punishment. His colleagues applaud wildly, completely unaware the speech is the ranting of a lunatic. When seen through his eyes, his colleagues – singing "Onward, Christian Soldiers" – appear to be rotting corpses. Their enthusiasm contrasts with the unfavourable reaction when Jack believed he was Christ. That night, he murders Grace for expressing her love for him. Her terrified scream is matched by the sound of a baby cooing "I'm Jack, I'm Jack", suggesting that their son – the Heir apparent – has inherited Jack's madness.

O'Toole held the rights to Barnes's play; Peter Medak approached O'Toole repeatedly about exercising those rights. According to Medak, the project got started one night that he and O'Toole were returning from the theatre, which "meant stopping at every pub between Soho and Hampstead, and it didn't matter if it was after closing hour because he would knock on the door and just say 'Peter's here,' and every door opened for him". Later on, at O'Toole's apartment, the deeply inebriated actor phoned his manager and said, "I'm with the crazy Hungarian and I know I'm drunk but I give you 24 hours to set this movie up." The next day, Medak received a call from United Artists and a deal was put together to shoot The Ruling Class.

Peter Barnes adapted the screenplay from his 1968 original, with few major changes. Filmed at the sprawling estate of Harlaxton Manor, with the interiors reconstructed on sound stages, the production cost $1.4 million, with O'Toole working for free (he was instead paid a great deal for the big-budget Man of La Mancha, released by the same studio later the same year).^{[citation needed]}