Rickenbacher Electro 
The famous guitar company was quite possiby the first major manufacturer to build an electric mandolin. How do I know? A picture of one (left) appears in their 1932 catalog, back when they were still known as the Electro String Instrument Corporation. By 1936–1938 the design had changed a bit, as we can see from the virtually mint-condition instrument on the right. By the time it was built, the company had changed its name to Rickenbacherówith an "h."
     In 1958 Rickenbacker made a dozen or so solidbody 8-string electrics (below left). Over the next 40 years or so, they became quite collectible and famously hard to find. In the late 1990s they were reintroduced and available again for a few years. The model number for the reissue (below right) was 5002V58. You'll notice that both the '58s and the reissues have a fret marker at the 9th rather than the 10th fretócorrect for guitars, bad for mandolins.