The history of Rokinon is quite unclear. I spent significant time searching various internet resources, but there is no solid evidence.
While Rokinon today solely refers to rebadged Samyang lenses, there may have been a time, when a presumably Japanese company called "Rokina Optical Company" existed. On the other hand a registered US trademark for the name "Rokinon" existed between the early 80ies until 2002 and was held by a company called "Rokina International".
However, I know of roughly 2 dozens of different 28/2.8 lenses all labeled "Rokinon":
Auto Macro Rokinon MC 1:2.8 f=28mm [KA], "Japan", 4 knobs rubber, very wide aperture ring
Auto Rokinon MC 1:2.8 f=28mm [KA], "Made in Japan", 3 rectangular knobs rubber
Auto Rokinon MC 1:2.8 f=28mm [KAR], "Made in Japan", 3 rectangular knobs rubber
Auto Rokinon MC 1:2.8 f=28mm [KAR], "Lens made in Korea", 3 knobs rubber
MC Auto Macro Rokinon 1:2.8 f=28mm [K], "???", 3 knobs rubber
MC Auto Macro Rokinon 1:2.8 f=28mm [KA], "Lens made in Japan", 6 knobs rubber, very wide aperture ring
MC Rokinon Wide-Auto F:2.8 f=28mm [K], "Lens made in Japan", 3 knobs rubber
MC Rokinon Wide-Auto F:2.8 f=28mm [K], "Lens made in Japan (?)", 3 rectangular knobs rubber
Rokinon 1:2.8 28mm MC [K], "Lens made in Japan", 2 vertical rectangular knobs rubber, shape of lens suggests Cosina origin
Rokinon 1:2.8 28mm MC [K], "Lens made in Japan", long vertical rectangular knobs rubber, shape of lens suggests Cosina origin
Rokinon Auto MC 1:2.8 f=28mm [K], "Lens made in Japan (?)", 3.5 knobs rubber, inscription around top end of barrel
Rokinon Auto MC 1:2.8 f=28mm [K], "Lens made in Japan", 4 rectangular knobs rubber, inscription around top end of barrel
Rokinon Auto SC 1:2.8 f=28mm [K], "Lens made in Japan", 4.5 knobs rubber
Rokinon Automatic 1:2.8 f=28mm [K], "Lens made in Japan", 6 knobs rubber
Rokinon Automatic Wide MC 1:2.8 f=28mm [K], "Lens made in Japan", 5.5 knobs rubber
Rokinon M.C 1:2.8 f=28 [K], "Korea", 6 knobs rubber, white engraving on aperture ring
Rokinon M.C 1:2.8 f=28 [K], "Korea", 6 knobs rubber, green engraving on aperture ring
Rokinon M.C 1.2.8 f=28mm [K], "Lens made in Korea", 6 knobs rubber
Rokinon MC 1:2.8 f=28mm [K], "Lens made in Japan", 4 knobs rubber
Rokinon MC 1:2.8 f=28mm [K], "Lens made in Japan", 4 knobs rubber, different aperture ring
Rokinon MC Auto1:2.8 f=28mm [K], "Japan (?)", 4 knobs rubber
Rokinon MC Automatic 1:2.8 f=28mm [K], "Lens made in Korea", 3 knobs rubber (looks identical to Sears 202.736890)
Rokinon MC Automatic 1:2.8 f=28mm [KAR], "Lens made in Korea", 3 knobs rubber (looks identical to Sears 202.7368000)
Rokinon Wide-Auto 1:2.8 f=28mm [KAR?], "???", 4 rectangular knobs rubber
Rokinon Wide-Auto 1:2.8 MC f=28mm [K], "Lens made in Japan", 3 knobs rubber
Bottom line: These 25 lenses most likely were made by multiple manufacturers, the question "how good is a Rokinon 28 f2.8" is impossible to answer.
As for the history of Rokina / Rokinon: I tend to believe that indeed there was at least a US company called Rokina which sold rebadged OEM stuff from Japan and Korea. I doubt that 40 years ago Samyang, as the first Korean lens producer, would have rebadged Japanese lenses. There even may have been a Japanese producer of lenses also called Rokina. The only thing we know for sure, is today Samyang holds and uses the Rokinon brand for their actual portfolio.
