Question: The man who composed the music for Thomas and the King was the Boston Pops' principal conductor during what years?

Context articles: The Nevill Feast
Tanglewood Festival Chorus
John Williams
Arthur Fiedler
Sleigh Ride
Thomas and the King
POPSearch
A Trumpeter's Lullaby
Russell Keable
Keith Lockhart

The Nevill Feast is a single-movement orchestral composition by the American composer Christopher Rouse.
 The work was commissioned by the Boston Pops Orchestra and completed in February 2003.
 It was first performed May 7, 2003 by conductor Keith Lockhart and the Boston Pops Orchestra, both to whom the work is dedicated.
The Tanglewood Festival Chorus, directed by James Burton, is a chorus which performs with the Boston Symphony Orchestra and Boston Pops in major choral works.
 The Tanglewood Festival Chorus (TFC) was organized in the spring of 1970, when founding conductor John Oliver became director of vocal and choral activities at the Tanglewood Music Center, the summer home of the BSO.
 Originally formed for performances at the BSO's summer home at the behest of the BSO's conductor designate Seiji Ozawa, the Tanglewood Festival Chorus is the official chorus of the Boston Symphony Orchestra and Boston Pops Orchestra year-round, performing in Boston, New York and Tanglewood.
John Towner Williams (born February 8, 1932) is an American composer, conductor, and pianist.
 With a career spanning over six decades, he has composed some of the most popular and recognizable film scores in cinematic history, including "Jaws", the "Star Wars" series, "Close Encounters of the Third Kind", "Superman", "E.T. the Extra-Terrestrial", the "Indiana Jones" series, the first two "Home Alone" films, the first two "Jurassic Park" films, "Schindler's List", and the first three "Harry Potter" films.
 Williams has been associated with director Steven Spielberg since 1974, composing music for all but three of his feature films.
 Other notable works by Williams include theme music for the Olympic Games, "NBC Sunday Night Football", "The Mission" theme used by NBC News, the television series "Lost in Space" and "Land of the Giants", and the incidental music for the first season of "Gilligan's Island".
 Williams has also composed numerous classical concertos and other works for orchestral ensembles and solo instruments.
 From 1980 to 1993, he served as the Boston Pops' principal conductor, and is now the orchestra's laureate conductor.
Arthur Fiedler (December 17, 1894 – July 10, 1979) was a long-time conductor of the Boston Pops Orchestra, a symphony orchestra that specializes in popular and light classical music.
 With a combination of musicianship and showmanship, he made the Boston Pops one of the best-known orchestras in the United States.
 Fiedler was sometimes criticized for over-popularizing music, particularly when adapting popular songs or edited portions of the classical repertoire, but he kept performances informal and sometimes self-mocking to attract a bigger audience.
"Sleigh Ride" is a popular light orchestral Christmas music standard composed by Leroy Anderson.
 The composer had the original idea for the piece during a heat wave in July 1946 and finished the work in February 1948.
 It was originally an instrumental piece; the lyrics, about someone asking another to join them for a ride in a sleigh, were written by Mitchell Parish in 1950.
 The orchestral version was first recorded in 1949 by Arthur Fiedler and the Boston Pops Orchestra.
 Sleigh Ride was a hit record on RCA Victor Red Seal 49-0515 (45 rpm) / 10-1484 (78 rpm), and has become a signature song for the orchestra.
 The 45 rpm version was originally issued on red vinyl.
 The Pops has also recorded the song with John Williams, their conductor from 1979 to 1995, and Keith Lockhart, their current conductor.
Thomas and the King is a stage musical with music by John Williams, lyrics by James Harbert, and a book by Edward Anhalt.
 It is based on the story of Thomas Becket and Henry II of England, and set in 12th century England.
 It opened at Her Majesty's Theatre London, 16 October 1975 to poor reviews and failed to make it to Broadway.
 The set was designed by Tim Goodchild.
 The musical was directed and choreographed by Norman Maen.
 The cast included James Smilie, Richard Johnson, Caroline Villiers, Martin McEvoy, and Dilys Hamlett.
POPSearch is the Boston Pops' nationwide talent competition that offers amateur singers the chance to perform with the orchestra at Boston's Fourth of July Extravaganza, as well as on the orchestra's national tour.
 The winner also receives a $5,000 cash prize.
 In its third year, the American Idol-style competition has expanded into a nationwide contest through video submissions on YouTube.com and voting through BostonPops.org.
 Deadline for applications is May 23.
 This year's competition opened on May 9, and the winner will be announced at the Boston Pops concert on June 28.
A Trumpeter's Lullaby is a short composition for solo trumpet and orchestra, written by American composer Leroy Anderson in 1949.
 The two and a half minute piece was premiered on May 9, 1950, by the Boston Pops Orchestra with Arthur Fiedler conducting and French-born American Roger Voisin as trumpet soloist.
 It was composed at the request of Voisin, who was principal trumpeter of the Boston Pops Orchestra at the time.
 It was first recorded on June 18, 1950, with Fiedler conducting Roger Voisin and the Boston Pops.
 Three months later it was recorded with Anderson himself conducting and James F. Burke as trumpet soloist.
 The first stereo recording was made in October 1956 with Frederick Fennell conducting the Eastman-Rochester Pops Orchestra, recorded in one take without rehearsal.
 The (uncredited) soloist was Sidney Mear.
Russell Keable is a British educator, composer and conductor.
 Keable studied conducting at the Royal College of Music with Norman Del Mar and later with George Hurst.
 Since 1983, he has been the principal conductor of London’s Kensington Symphony Orchestra, since 2004, the principal conductor of the City of Peterborough Symphony Orchestra and since 2006, the principal conductor of the University of Surrey’s University Symphony Orchestra and Choir.
 Since 2006, Keable has taught conducting at the University of Surrey.
Keith Alan Lockhart (born November 7, 1959) is the Conductor of the Boston Pops Orchestra, and the Principal Conductor of the BBC Concert Orchestra.
 Lockhart was the Music Director of the Utah Symphony from 1998 - 2009, and has held honorary titles in many other orchestras.