Ferdinand Rebay (June 11, 1880 – November 6, 1953) was an Austrian composer, music teacher, choir director, and pianist.
His life and work can be read about in detail in the sources listed above.
It is astonishing how many works he composed for guitar and/or ensembles featuring guitar, and how little of it is freely available. However, a few pieces can be found on the internet. The sonatas and other larger works are only available for purchase.
But there is still a lot to discover.