Gustaf Allan Pettersson (19 September 1911 – 20 June 1980) was a Swedish composer and violist. He is considered one of the 20th century's most important Swedish composers and was described as one of the last great symphonists, often compared to Gustav Mahler.: 3 His music can hardly be confused with other 20th-century works. In the final decade of his life, his symphonies (typically one-movement works) developed an international following, particularly in Germany and Sweden. Of these, his best known work is Symphony No. 7. His music later found success in the United States.
https://en.wikipedia.org/wiki/Allan_Pettersson