Asahi Optical was a japanese firm that made eyeglass lenses, binoculars, and other optical equipment before and during World War II. After that they added cameras to the list. Their camera line is (at least in the US) called Pentax. In the US, Honeywell imported it for many years, so cameras from the 50s, 60s and early 70s are usually branded Honeywell Pentax, whereas later ones are Asahi Pentax or simply Pentax.
Famous company—one of the first Japanese companies to break away from making Leica-copies and into SLRs, especially those that didn't look like German ones. They offered a number of firsts or near-firsts, lost the pro-market (at least in the US) to Nikon, but fared much better in the advanced-amateur market. Their bread-and-butter was the Spotmatic, one of the first to have the meter inside the camera and sensing the light through-the-lens (TTL), so the meter saw the same light the film saw. The original prototype was a spotmeter, thereby giving it the name, but the production model was an averaging meter.
Pentax had huge success with the 42mm screw-mount, which was originated by the East German company Praktica, so much so that the mount is often called the Pentax Universal Screw Mount, even though Praktica, Mamiya, Miranda, Zenit and many other companies used the same mount. The Spotmatic and its successors used the screw-mount. These days it's typically called the M42 screw-mount.
But by the early 70s most of the camera makers (at least the Japanese ones) had quit using screw-mounts and were going to bayonet. Pentax offered theirs as a universal mount, and it's sometimes called the Pentax Universal Mount, but I don't know anyone who uses it. By the time Pentax created it, the other big Japanese firms like Nikon, Canon and Minolta had already made their own and sold far too many cameras to abandon it simply so people could inter-change their lenses. Besides, the likes of Nikon and Canon made nice money selling lenses to fit their cameras and licensing their bayonet mounts to the 3rd party makers.
Regardless, Pentax introduced a number of new cameras using the new mount, including an updated version of their ubiquitious Spotmatic, which they called the K-1000. It too was a huge seller.
The K-1000 was the entry-level at the time, an all-metal, all mechanical machine in an age where everything was going automatic. 1976 was the year of the Canon AE-1, which had semi-automatic exposure, a lot of plastic parts and an electro-magnetic shutter, making it light and compact, and it sold big. Later cameras would go the way of the AE-1 and away from the mechanical route.
But the K-1000 found a niche as a great student camera, since photo students have to learn how to set exposures without relying on automation. Plus the camera was a workhorse, didn't have flakey electronics, would run even if the battery were dead, and had Pentax's name and reputation of excellence to back it up. The result was an incredibly long run for a Japanese camera in the modern era.
Mine is a flea-market find. It had been dropped badly so it was super cheap. If you look at it from the bottom, you can see the lens mount and lens sit slightly off perpendicular to the film plane. The shutter is also a bit off—it labors to fire. You push the button and it'll fire—eventually.
Camera manual: Orphan Cameras.com