The Aberman “Million Dollar” .45 Luger. Two .45 caliber prototypes were originally manufactured by DWM under the supervision of Georg Luger for the U.S. Trials of 1906, but neither is known to have survived.
At least two revised pistols with a different grip angle were made shortly afterward for possible commercial or military sales. One is in the Norton Art Gallery in Shreveport, Louisiana, and this is the other, sold in 2010 to a private collector.
I found this also very interesting to read more about this item.