Jean Sibelius
Jean Sibelius ( ; ), born Johan Julius Christian Sibelius (8 December 186520 September 1957), was a Finnish composer and violinist of the late Romantic and early-modern periods. He is widely recognized as his country's greatest composer and, through his music, is often credited with having helped Finland to develop a national identity during its struggle for independence from Russia.
Jean Sibelius
The core of his oeuvre is his set of seven symphonies, which, like his other major works, are regularly performed and recorded in his home country and internationally. His other best-known compositions are "Finlandia", the "Karelia Suite", "Valse triste", the Violin Concerto, the choral symphony "Kullervo", and "The Swan of Tuonela" (from the "Lemminkäinen Suite"). Other works include pieces inspired by nature, Nordic mythology, and the Finnish national epic, the "Kalevala", over a hundred songs for voice and piano, incidental music for numerous plays, the opera "Jungfrun i tornet" ("The Maiden in the Tower"), chamber music, piano music, Masonic ritual music, and 21 publications of choral music.
Cecil Gray (composer)
Born in Edinburgh, he took an arts degree at the University of Edinburgh and studied composition privately with the Anglo-Canadian composer Healey Willan. From there he developed his career as editor, music critic, and author. Gray first met Philip Heseltine (another writer/critic who also composed music under the name Peter Warlock) at the Cafe Royal in the spring of 1916 and they were soon sharing a studio – 2 Anhalt Studios, close to Battersea Park. This led to Gray's first musical venture, the co-sponsoring with Heseltine in 1917 of a concert of works by the then completely unknown composer Bernard van Dieren. Three years later Gray co-founded the early music periodical "The Sackbut", also with Heseltine. Gray subsequently worked as music critic for publications including "The Daily Telegraph", "The Manchester Guardian", and "The Morning Post", and occasionally for the "Radio Times" and "The Listener".
Cecil Gray (composer)
His first published book, "A Survey of Contemporary Music", was published in 1924, and was notable for its contrary opinions. Frank Howes, "The Times" chief music critic, pointed out that the formula "so far from the usual view being true, the precise opposite is the case" occurs every few pages. With Heseltine, Gray co-authored the characteristically perverse "Carlo Gesualdo, Prince of Venosa: Musician and Murderer" in 1926. A full, but equally unorthodox "History of Music" followed in 1928. Gray was also an early advocate of Sibelius, championing his music in the UK from 1923 when it was still all but unknown there. He wrote two books on the composer in 1931 and 1935. His sympathetic portrayal of Heseltine/Warlock in his memoir of 1934 is thought by many to be his best literary work. There were also two collections of essays, "Predicaments" (1936) and "Contingencies" (1947), a play about Gilles de Rais and an autobiography, "Musical Chairs" (1948).

Question: Who is this Finnish composer and violinist of the late Romantic and early-modern periods that the Scottish music critic and composer Cecil Gray published books on?
Answer: Jean Sibelius