Henri Dutilleux (1916-2013)
The French composer Henri Dutilleux went to school with my grandfather. For me his music is extraordinary, because of the way he designs chords to sound sensuous, resonant and colourful. Maxime Joos has written a book (in French) on the relationships between what Dutilleux does with rhythm and how his music is perceived.
My favourite pieces by Dutilleux are Métaboles (1964), the enchanting violin concerto l'Arbre des songes (1985) and Mystère de l'instant (1989). He has also written some beautiful piano music. See The Guardian's Guide to Dutilleux's Music.