This is actually the pseudonym used by Johan Christian Kammen, (there is no record of him ever changing his name?), an early luthier/inventor who worked out of Washington State from 1895 until 1914 when he moved to Los Angeles, (where he resided until his death in 1930). He is the man who if not invented, (there are some earlier obscure instruments like the Torban that had some similarities?), designed and patented Harp Guitars, Mandolins and Ukuleles. He is also the real inventor, (again things like Dulcimers shared similarities with the design so "inventor" might be stretching it a bit far?) of the hollow square necked Lap Steel Guitar that has come to be known as the Weissenborn.

His quality of luthiery was known to be a bit erratic with the use of short cuts like screws to overcome the difficult bits, and that, certainly, with the Ukuleles, no two looked the same! It is also the case that he got other people, particularly Otto Andersen a cabinet maker from Seattle, and possibly Hermann Weissenborn, to make some of the instrument too. 

Back the the Ukuleles, He is know to have made, (or at least have made for him?) at least 35 Harp Ukuleles and 5 Harp Taropatches. I have never heard of any non Harp Ukuleles or of any Lap Steel Ukuleles made or branded by him. He did have some sort of distribution deal with Buegeleisen & Jacobson for his instruments and there are advertisements that B&J put out saying they would take over and mass produce Knutsen designed Harp Ukuleles but none have been found and beyond the advertisements there is no evidence of the production ever having taken place? He also had some kind of deal in place with Ernest Ka'ai for distribution of his instruments in Hawaii, (there is no evidence of the Ka'ai factory making any though).