Question: Who is the psychoanalyst after which psychoanalyst author and trainer John Steiner has been called "a prolific London post-Kleinian"?

Context paragraphs:
Frederick (horse): Frederick (1826–1837) also known as "Frederic", was a British Thoroughbred racehorse and sire.  In a career that lasted from June 1829 to August 1831 he ran five times and won once.  His only win came on his racecourse debut, when he recorded an upset victory in the 1829 Derby ridden by his sixty-year-old trainer John Forth.  Frederick failed to reproduce his Derby-winning form, finishing no better than third in four subsequent races.

James Anthony (psychoanalyst): Elwyn James Anthony or "James Anthony" or "E. James Anthony", M.D., D.P.M. (21 January 1916 – 10 December 2014) was a British psychoanalyst and was best known for his work on resilience and invulnerability/risk in children, particularly those whose parents had serious mental illnesses.  He was one of two founders -with S. H. Foulkes- of the field of group psychotherapy.  A prolific writer, he authored 320 research articles and 18 books, many of which were translated into other languages.  James Anthony was a training psychoanalyst who studied in London where he began a distinguished career as a child psychotherapist and psychiatrist.  He studied child development under Jean Piaget and, after leaving the Maudsley Hospital, occupied the Ittleson Chair of Child Psychiatry, at Washington University School of Medicine, St. Louis.  He later became Director of Psychotherapy at Chestnut Lodge, where he developed a program of group psychotherapy for adolescent inpatients.

David Morgan (psychoanalyst): David Howell Morgan (BAHons D.Clin.Psych.  FBPAS FPBPA SMBPF.  Training Analyst Supervisor IPA.  AMBPS.  MBPC) is a psychoanalyst and consultant psychotherapist who has worked at the Portman Clinic London for 25 years.  He went on to specialise in patients' presenting with problems around sexuality and violence.  Morgan co-edited a popular textbook on sexuality, perversion and delinquency.  He is now a psychoanalyst and consultant seeing private patients and provides consultations to political groups.  He is chair of the Political Minds Seminars at the British Psychoanalytic Society.  He regularly contributes to radio and television and lectures nationally and internationally.  Morgan’s recent research has focused on the psychological implications for whistleblowers and the conditions, socially, politically, and psychologically under which a person may "turn a blind eye" or take on the responsibility of whistleblowing.  He also presents a podcast called "Frontier Psychoanalyst" on BBC i-player.  

Sir Martin: Sir Martin (1906–1930) was a Thoroughbred racehorse that was foaled in 1906 in Lexington, Kentucky at Hamburg Place, the stud farm of noted turfman and horse trainer John E. Madden.  Sir Martin was a half brother to the first Triple Crown winner Sir Barton, and he raced in the United States, Great Britain and France.  Sir Martin was the betting favorite for the 1909 Epsom Derby, but stumbled and threw his jockey at the Tattenham Corner turn, allowing King Edward VII's horse Minoru to win.

John Steiner: John Steiner (born 7 January 1941 in Chester, Cheshire) is an English actor.  Tall, thin and gaunt, Steiner attended the Royal Academy of Dramatic Arts and worked for a few years at the BBC.  Steiner featured in a lead role in a television production of "Design for Living" by Noël Coward.  Later he found further work primarily in films including "Marat/Sade" (1967), and the original "Bedazzled" (1967) with Peter Cook and Dudley Moore.  In 1969, Steiner was hired to play a part in the spaghetti western "Tepepa", and also appeared opposite Franco Nero in "White Fang", directed by Lucio Fulci.  He found himself in demand in Italy and moved there, appearing in a great number of Italian exploitation and B-films including police actioners ("Violent Rome"), westerns ("Mannaja"), war films ("The Last Hunter"), nazisploitation ("Deported Women of the SS Special Section"), sci-fi adventure films ("Yor, the Hunter from the Future"), and horror films, such as Mario Bava's "Shock", Dario Argento's "Tenebrae", and Ruggero Deodato's "Body Count".  He also became a favourite of famed Italian filmmaker Tinto Brass, featuring in "Salon Kitty", the infamous "Caligula", "Action", and "Paprika".

Melanie Klein: Melanie Reizes Klein (30 March 1882 – 22 September 1960) was an Austrian-British psychoanalyst who devised novel therapeutic techniques for children that influenced child psychology and contemporary psychoanalysis.  She was a leading innovator in object relations theory.

Sherrill W. Ward: Sherrill W. Ward (March 14, 1911 - February 23, 1984) was an American Hall of Fame Thoroughbred racehorse trainer.  Born in Miami, Florida, he was the son of trainer John Sherrill Ward.  His brother, John T. Ward, also trained horses and ran Fort Springs Farm in Lexington, Kentucky.  Having learned the business from his father, in 1929 Sherrill Ward embarked on a training career of his own.

John M. Gaver Jr.: John Milton "Jack" Gaver Jr. (September 17, 1940 – January 15, 2002) was an American trainer of Thoroughbred racehorses.  He was the son of National Museum of Racing and Hall of Fame trainer John M. Gaver Sr., who was head trainer for the Whittney family's Greentree Stable for 38 years.  In 1977 his father suffered a stroke and John Jr. took over his responsibilities at Greentree where he would remain for the next fifteen years.  For Greentree he trained back-to-back Champions Late Bloomer in 1978 and Bowl Game in 1979.

William Scott (jockey): William Scott (1797–1848) was a British jockey.  Known as "Bill", he was a brother of the renowned trainer John Scott who frequently conditioned horses that he rode.

John Steiner (psychoanalyst): John Steiner is a psychoanalyst, author and trainer at the British Psychoanalytical Society.  Steiner, a 'prolific London post-Kleinian', is best known for his conceptions of the "pathological organisation" or the "psychic retreat"...between the paranoid-schizoid and the depressive positions'.  His book "Psychic Retreats" describes a treatment methodology for patients with complex defence mechanisms that are difficult to treat with conventional psychoanalysis.

Supporting paragraphs: John Steiner (psychoanalyst) Melanie Klein
Answer: Melanie Reizes Klein