Leo Sowerby (1895 – 1968) is described in the booklet notes of a new Cedille album of his compositions ( Leo Sowerby: The Paul Whiteman Commissions and Other Early Works ) as “already the most frequently performed classically trained American composer” by the 1920s.
He certainly was prolific; the booklet goes on to claim that Sowerby had written some 550 pieces by the time of his death. His music was regularly played by his hometown Chicago Symphony under Frederick Stock. He even won a Pulitzer in 1946 — not that winning that prize is a guarantee of immortality. Yet his name hardly ever comes up in discussions about the leading American composers of his time.