It is the Steyr Hahn ("Steyr hammer" model), adopted by the Austrian army as the Model 1911. The original chambering is the 9mm Steyr, a longer round than the 9mm Luger, but equivalent in power. The 9mm Steyr is similar to the 9mm Largo, but I do not consider them interchangeable.
The gun is a locked breech, recoil operated pistol, operating by means of a rotating barrel, a perfectly good system. They are rugged and reliable pistols and were used throughout the old Austro-Hungarian Empire through two World Wars. Many were used by German police and reserve forces in WWII, and quite a few of those were rebarrelled to 9mm Parabellum (9mm Luger). Converted guns have an "08" on the side of the slide.
There are two somewhat weak points. One is that the recoil spring is a flat coil, which sometimes breaks; it can be replaced with a conventional round wire spring of the right diameter and tension. The second drawback is that to load efficiently requires a clip ("stripper" clip); otherwise it has to be loaded one round at a time, a slow process. Clips are available from time to time.
That gun appears to have been reblued, but they are scarce enough that it is still a desirable collector gun. They generally run from $300 to $600 depending on condition, but I see some for sale for more (though I suspect the seller won't get his inflated price). I would guesstimate yours at around $450, retail.
Jim