Panther was a small, specialist motorcycle company, best known for their big "Sloper" bikes desgined primarily for sidecar use. The name came from the layout, where the cylinder followed the angle of the front downtube. The engine may even have been integrated into the frame structure.
They had a big, single-cylinder engine, 650cc I think, and may have been the side-valve type (L-head for our US readers) through to the end. They disappeared from the market place in the early 1960s. I'm not sure they ever exported the "Sloper"to the US.