I love the low horn etudes by Hermann Neuling; I feel certain that these made a big difference in my playing. I have had most of my students work out at least a few of the 30 Spezial-Etuden fur tiefes Horn [30 Special Etudes for Low Horn] published by Pro Musica Verlag, and a couple students have also worked on the Bagatelle for horn and piano, which is a standard work requested on European low horn auditions. However, I have never been able to say much more about him as a person other than he was an early twentieth century low horn player in Germany.
Recently the horn list was to the rescue with his dates (1897-1967) and confirmation of some basics on his career that are posted in the Wikipedia, not my favorite source but sometimes that is all we have. To quote the article there,
He was engaged for many years as a low horn player at the Staatsoper Unter den Linden in Berlin and taught at the Conservatorium nearby…. Neuling was also a member of the Bayreuth Wagner Festival orchestra 1931-64.
Check out the 30 etudes, especially volume 2, these will help you not only master low range production but also the reading of old notation bass clef.