His early music was inspired by composers such as Johannes Brahms and Edvard Grieg, but he soon developed his own style, first experimenting with progressive tonality and later diverging even more radically from the standards of composition still common at the time.

Nielsen was born on 9 June 1865, the seventh of twelve children in a poor peasant family, at Sortelung near Nørre Lyndelse, south of Odense on the island of Funen.

His mother, whom he recalls singing folk songs during his childhood, came from a well-to-do family of sea captains,[2] while one of his half-uncles, Hans Andersen (1837–1881), was a talented musician.

[7] The army paid him three kroner and 45 øre and a loaf of bread every five days for two and a half years, after which his salary was raised slightly, enabling him to buy the civilian clothes he needed to perform at barn dances.

[11][15] Between graduation and attaining this position, he made a modest income from private violin lessons while enjoying the continuing support of his patrons, not only Jens Georg Nielsen but also Albert Sachs (born 1846) and Hans Demant (1827–1897) who both ran factories in Odense.

[18] According to Fanning, their relationship was not only a "love match", but also a "meeting of minds"; Anne Marie was a gifted artist and a "strong-willed and modern-minded woman, determined to forge her own career".

[19] This determination would strain the Nielsens' marriage, as Anne Marie would spend months away from home during the 1890s and 1900s, leaving Carl, who pursued extramarital affairs with other women in her absence, to raise their three young children in addition to composing and fulfilling his duties at the Royal Theatre.

[19] Fanning writes, "At this time his interest in the driving forces behind human personality crystallized in the opera Saul and David and the Second Symphony (The Four Temperaments) and the cantatas Hymnus amoris and Søvnen".

[19] Carl suggested divorce in March 1905 and had considered moving to Germany for a fresh start,[21] but despite several extended periods of separation the Nielsens remained married for the remainder of the composer's life.

Irmelin, the elder daughter, studied music theory with her father and in December 1919 married Eggert Møller (1893–1978), a medical doctor who became a professor at the University of Copenhagen and director of the polyclinic at the National Hospital.

[25] The composer was particularly upset in the 1920s when his long-standing Danish publisher Wilhelm Hansen was unable to undertake publication of many of his major works, including Aladdin and Pan and Syrinx.

[33] In his Lives of the Great Composers, the music critic Harold C. Schonberg emphasizes the breadth of Nielsen's compositions, his energetic rhythms, generous orchestration and his individuality.

The musicologist Niels Krabbe describes the popular image of Nielsen in Denmark as being like "the ugly duckling syndrome" – a reference to the tale of the Danish writer Hans Christian Andersen – whereby "a poor boy ... passing through adversity and frugality ... marches into Copenhagen and ... comes to conquer the position as the uncrowned King".

[41] To non-Danish critics, Nielsen's music initially had a neo-classical sound but became increasingly modern as he developed his own approach to what the writer and composer Robert Simpson called progressive tonality, moving from one key to another.

"[45] Nielsen's philosophy of music style is perhaps summed up in his advice in a 1907 letter to the Norwegian composer Knut Harder: "You have ... fluency, so far, so good; but I advise you again and again, my dear Mr.

It fully exploits Nielsen's technique of confronting two keys at the same time and includes a peaceful section with soprano and baritone voices, singing a tune without words.

Performed by the Danish Radio Symphony Orchestra conducted by Erik Tuxen at the 1950 Edinburgh International Festival, it caused a sensation, sparking interest in Nielsen's music outside Scandinavia.

[53][54] Generally considered to be Denmark's national opera, in its home country it has enjoyed lasting success and popularity, attributable to its many strophic songs, its dances and its underlying "old Copenhagen" atmosphere.

Writing in the newspaper Dannebrog, Nanna Liebmann referred to the work as "a decisive victory" for Nielsen, and Angul Hammerich of Nationaltidende welcomed its improved clarity and purity.

18, Nielsen's second major choral work, sets to music the various phases of sleep including the terror of a nightmare in its central movement which, with its unusual discords, came as a shock to the reviewers at its premiere in March 1905.

[70] The Rhapsodic Overture, An Imaginary Trip to the Faroe Islands (En Fantasirejse til Færøerne), draws on Faroese folk tunes but also contains freely composed sections.

Over the years, Nielsen wrote the music for over 290 songs and hymns, most of them for verses and poems by well-known Danish authors such as N. F. S. Grundtvig, Ingemann, Poul Martin Møller, Adam Oehlenschläger and Jeppe Aakjær.

[91]Of great significance was Nielsen's contribution to the 1922 publication, Folkehøjskolens Melodibog (The Folk High School Songbook), of which he was one of the editors together with Thomas Laub, Oluf Ring and Thorvald Aagaard.

[97] Within two months of its successful premiere at the Odd Fellows Concert Hall in Copenhagen on 28 February 1912, the Third Symphony (Espansiva) was in the repertoire of the Amsterdam Concertgebouw, and by 1913 it had seen performances in Stuttgart, Stockholm and Helsinki.

[105] In 1988 Nielsen's diaries and his letters to Anne Marie were published, and these, together with a 1991 biography by Jørgen Jensen using this new material, led to a revised objective assessment of the composer's personality.

[106] Writing in The New York Times on the occasion of Nielsen's 125th anniversary in 1990, the music critic Andrew Pincus recalled that 25 years earlier Bernstein had believed the world was ready to accept the Dane as the equal of Jean Sibelius, speaking of "his rough charm, his swing, his drive, his rhythmic surprises, his strange power of harmonic and tonal relationships – and especially his constant unpredictability" (which Pincus believed was still a challenge for audiences).

[107] Biographies and studies in English in the 1990s[108] helped to establish Nielsen's status worldwide,[109] to the point at which his music has become a regular feature of concert programming in Western countries.

[114] There are now numerous recordings of all Nielsen's major works, including complete cycles of the symphonies conducted by, amongst others, Sir Colin Davis, Herbert Blomstedt and Sakari Oramo.

[121] His image was selected in recognition of his contribution to Danish music compositions such as his opera Maskarade, his Espansiva symphony and his many songs including "Danmark, nu blunder den lyse nat".

In addition to many performances in Denmark, concerts were programmed in cities across Europe, including London, Leipzig, Kraków, Gothenburg, Helsinki and Vienna, and even further afield in Japan, Egypt and New York.