J.V. Der Roost, a prominent figure in 20th-century jazz, was a Belgian arranger renowned for his sophisticated contributions to big band and orchestral jazz. Active from the mid-century onward, Der Roost's style blended traditional swing elements with contemporary harmonic and rhythmic innovations. He gained acclaim for his intricate arrangements for ensembles like the Metropole Orchestra and various European radio big bands, often featuring his unique voicings and contrapuntal textures. His work significantly expanded the repertoire and technical demands of jazz ensembles, influencing generations of arrangers and solidifying his legacy as a master of the craft.