Question: Who wrote the novel that became the source material for this musical in which the American stage actor Matt Harrington played Mr. Wormwood?

Context articles: The Mr. Men Show
Mr. Pip
Russell Harvard
Adrift in Soho
List of human Sesame Street characters
Al Harrington
Matt Harrington (actor)
Mr. Noodle
Matilda the Musical
John Harrington (American football)

The Mr. Men Show (sometimes simply called Mr. Men) is a British/American  animated television series based on the original "Mr. Men and Little Miss" books created in the late 20th century by British author Roger Hargreaves and his son Adam Hargreaves.
 Adapted from the published source material into a television variety program, "The Mr. Men Show" features comedy sketches (primarily), pantomimes, dance numbers and music videos.
 The TV series is directed by Mark Risley and executive produced by Eryk Casemiro with Kate Boutilier.
 Original score and songs are composed by Jared Faber.
 The series originally aired on Channel 5's Milkshake!
 programming block in the United Kingdom and Cartoon Network in the United States.
Mr. Pip is a 2012 New Zealand film, set in Papua New Guinea, based on Lloyd Jones' novel "Mister Pip".
 Andrew Adamson wrote the film adaption, which he also directed.
 Hugh Laurie played Mr. Watts.
Russell Wayne Harvard (born April 16, 1981) is an American actor.
 He made his feature film debut in Paul Thomas Anderson's "There Will Be Blood" (2007), playing opposite Daniel Day-Lewis as his adopted grown son, H.W. Plainview.
 In the 2010 biopic "The Hammer", he portrayed deaf NCAA championship wrestler and UFC mixed martial arts fighter Matt Hamill.
 Harvard also won acclaim Off Broadway in 2012 as Billy, the deaf son in an intellectual, though dysfunctional, hearing British family, in "Tribes" by Nina Raine.
 For his interpretation, he won a 2012 Theatre World Award for Outstanding Debut Performance and nominations for Drama League, Outer Critics Circle and Lucille Lortel Awards for Outstanding Lead Actor.
 He played Mr. Wrench in the first and third season of the television series "Fargo".
Adrift In Soho is a novel by Colin Wilson.
 It was first published in England in 1961 by Victor Gollancz.
 The novel describes the English beat generation.
 The novel was republished to great acclaim by New London Editions in 2011, when Cathi Unsworth wrote 'Adrift in Soho is currently in production by Burning Films and with such rich source material, perhaps Wilson will now receive some contemporary reassessment for his continuing fascination with the human condition and the wit, warmth and insight that he brings to his accounts of those he has shared his unusual journeys with.'
Since the premiere of the children's television program "Sesame Street" on November 10, 1969, it has included what writer Malcolm Gladwell has called "the essence of "Sesame Street"—the artful blend of fluffy monsters and earnest adults".
 The original cast, chosen by original producer Jon Stone, consisted of four human actors—Matt Robinson, who played Gordon; Loretta Long, who played Gordon's wife, Susan; Will Lee, who played Mr. Hooper; and Bob McGrath, who played Bob.
 Unlike most children's television programs at the time, the producers of "Sesame Street" decided against using a single host and cast a group of ethnically diverse, primarily African American actors/presenters, with, as "Sesame Street" researcher Gerald S. Lesser put it, "a variety of distinctive and reliable personalities".
Albert "Al" Harrington (born February 17, 1980) is an American professional basketball player who last played for the Sydney Kings of the National Basketball League (NBL).
 Selected with 25th overall pick in the 1998 NBA draft, Harrington played 16 seasons in the National Basketball Association (NBA) for the Indiana Pacers, Atlanta Hawks, Golden State Warriors, New York Knicks, Denver Nuggets, Orlando Magic and Washington Wizards.
 He also spent a short stint with the Fujian Sturgeons of the Chinese Basketball Association (CBA).
Matt Harrington is an American stage actor, best known for his work in the Broadway production of Matilda the Musical, in which he replaced Tony Award winner Gabriel Ebert in the role of Mr. Wormwood.
When Irwin became unavailable, Sherman asked Michael Jeter, who was her friend, to replace Irwin as Mr. Noodle's brother Mister Noodle, which he accepted enthusiastically, calling it his favorite role in twenty years.
 Jeter was in the role beginning in 2000, until his death in 2003.
 Kristin Chenoweth played Mr. Noodle's sister Ms. Noodle, and Sarah Jones played Mr. Noodle's other sister Miss Noodle.
 As of January 2017, Daveed Diggs and comedian Daniel Koren, have played two more of Mr. Noodle's brothers.
 Five actors playing members of the Noodle family have won Tonys.
Matilda the Musical is a stage musical based on the 1988 children's novel of the same name by Roald Dahl.
 It was adapted by Dennis Kelly, with music and lyrics by Tim Minchin.
 The musical's narrative centres on Matilda, a precocious 5-year-old girl with the gift of telekinesis, who loves reading, overcomes obstacles caused by her family and school, and helps her teacher to reclaim her life.
 After a twelve-week trial run staged by the Royal Shakespeare Company (RSC) at Stratford-upon-Avon from November 2010 to January 2011, it received its West End premiere on 24 November 2011 at the Cambridge Theatre and its Broadway premiere on 11 April 2013 at the Shubert Theatre.
John Patrick Harrington (April 15, 1921 – January 8, 1992) was a professional American football end and defensive end who played two seasons for the Cleveland Browns and Chicago Rockets in the All-America Football Conference.
 Harrington attended Marquette University and became the football team's captain in 1942.
 He joined the military in 1944 and played for Air Force teams in 1944 and 1945.
 He was drafted by the Chicago Cardinals in 1945 but instead signed with the Browns before the team's inaugural season in 1946.
 Harrington played in one season for the Browns before he was traded to the Rockets in 1947.