Eugène Dhers was a hard working French professional cyclist, riding the Tour de France 11 times between 1914 and 1927.

His name is listed on this site as a derailleur brand because, in 1938, he applied for a patent for a very complete and sophisticated design of derailleur. The technical drawings attached to the patent application are too detailed and too professionally produced to have been made without, at least, the production of numerous well finished prototypes. Crucially the design incorporates a paralleloigram.

I cannot find a listing of a cycle company associated with Eugène Dhers, so I do not know what happened to his design. He was born in Gennevilliers, a suburb of Paris, and appears to have lived in Paris throughout his life - so that is where I suspect that his deraileur may have been created and/or manufactured.