This is a bowie-style hunting knife made in Solingen, Germany, in the 1950s or 1960s. The marking out on the blade (Original Bowie Knife) was widely used during that time period, on hunting knives made in Germany for export to the U.S.
I suspect (but I am not certain) that this "Buffalo Brand" drawn to look like a buffalo belonged to the Missoula Mercantile Co of Montana, and was last used in 1972. This firm would have imported and sold the knife.
Where do you find the word RUKO?
For additional information, please visit my Knife questions page.
Be advised that this knife is not worth much more than my appraisal fee.