William L. Lange was in business as a banjo maker from 1897 until 1939. The company started in New York as Rettberg & Lange with William Rettberg as the other partner, but in April 1922, William L. Lange took over sole control of the company and changed the name to Wm. L. Lange. They had their own range of Banjos and Banjoleles , notably Paramount, Solo, Orpheum and Banner Blue, (plus a few others and some brands were not used on Banjoleles), but they also produced models for big distributors like Bruno and Henry Stadlmair, (for whom they made the Avalon.) They also sold parts, like necks and metalwear, for others like Majestic to use when making their own Banjo instruments. 

In 1925 they opened a second factory in Brooklyn for the production of more budget Banjos notably the Langestile, the Blue Boy, Tourraine and possibly the Challenger, (I have read that this was an OEM brand for someone else but I don't know who?). I have also seen a number of Banjoleles with no name on the headstock just a heart, or more usually a 5 pointed star, (Used by other makers as well to make identification hard).

Lange Banjos often have a very distinctive headstock, and the the higher quality models often "interesting" fret markers. Other brand names Lange used on Banjo instruments but not necessarily Ukulele Banjos are Auditorium, (Rettberg & Lange), Artcraft, (maybe another OEM), Orchestra King, Randl, (drums?), Supertone, (pre Harmony, or another OEM name?) To the best of my knowledge Lange never made any Ukuleles or other all wood chordophones, (I have read that the output of both factories was exclusively Banjo Instruments), though Martin famously made some, (32), very odd looking Guitars and Tenor guitars with a kind of extended resonator back for them under the Paramount brand name.