Task: Question Answering
Input (English): Passage: At the outbreak of the First World War, Holst tried to enlist but was rejected as unfit for military service. He felt frustrated that he could not contribute to the war effort. His wife became a volunteer ambulance driver; Vaughan Williams went on active service to France as did Holst's brother Emil; Holst's friends the composers George Butterworth and Cecil Coles were killed in battle. He continued to teach and compose; he worked on The Planets and prepared his chamber opera Savitri for performance. It was first given in December 1916 by students of the London School of Opera at the Wellington Hall in St John's Wood. It attracted no attention at the time from the main newspapers, though when professionally staged five years later it was greeted as "a perfect little masterpiece." In 1917 he wrote The Hymn of Jesus for chorus and orchestra, a work which remained unperformed until after the war.In 1918, as the war neared its end, Holst finally had the prospect of a job that offered him the chance to serve. The music section of the YMCA's education department needed volunteers to work with British troops stationed in Europe awaiting demobilisation. Morley College and St Paul's Girls' School offered him a year's leave of absence, but there remained one obstacle: the YMCA felt that his surname looked too German to be acceptable in such a role. He formally changed "von Holst" to "Holst" by deed poll in September 1918. He was appointed as the YMCA's musical organiser for the Near East, based in Salonica. 
Question: Who changed their surname?
Output (English): Holst.