During the Second World War, Alexander Zwaap had to hide his identity by living under an alias, and in 1953, he legally changed his name to that alias, Lex van Delden. His life story is impressive, although he never spoke of the traumatic events he experienced during the war years, which he overcame with tremendous courage and resilience. Music was for him, as he often put it, a ‘transfer medium between people’. He took this approach with his compositions, since he wanted his music to communicate with its audience. Van Delden was a committed advocate for Dutch music and his social commitment was equally borne out in his readiness to hold several administrative posts, including the presidency of the Society of Dutch Composers (GeNeCo) and the chairmanship of the Bureau voor Muziekauteursrecht (Buma), the Dutch Performing Rights Organisation.

Alexander Zwaap was born on 10 September 1919 in the Jewish quarter of Amsterdam, on the Recht Boomssloot. He was the only child of Wolf and Sara Zwaap, who shared a house with his grandparents. The family was not Orthodox Jewish. As a youngster, he loved playing for the Amsterdam football club Ajax. Even during his medical studies, football remained an intrinsic part of his life. He never missed any of the club's competition games and became a regular in the Ajax boardroom. In the 1960s he wrote a weekly column about football, ‘From the stands, from the fields’, for Het Parool.

Zwaap's father was a teacher at a Jewish school and had worked with a colleague on operettas for children. He was also an amateur violinist, but there wasn't much music-making at home, although the family regularly went to the volksconcerten (‘people's concerts’). At the age of seven, he began piano lessons, initially with Martha Zwaga and later with the pianist Cor de Groot, who was only five years his senior but already a rising star.

Once while bedridden, he began jotting down some notes. It was a pleasant way to pass the time. In spite of his artistic promise (at the age of sixteen, he had a part-time job as a ballet accompanist), his ambition was to become a neurosurgeon, and in 1938 he enrolled at the Municipal University of Amsterdam to study medicine.