Korean yen
The Korean yen was the currency of Korea between 1910 and 1945. It was equivalent to the Japanese yen and consisted of Japanese currency and banknotes issued specifically for Korea. The yen was subdivided into 100 sen. It replaced the Korean won at par and was replaced by the South Korean won and the North Korean won at par.
North Korean won
As explained above, there are two varieties of foreign certificates. For the 1978 banknote series, foreign certificates, called "Pakkundon", meaning "exchangeable money" were implemented by an overstamp and serial number color. This was intended to protect the value of the national currency in North Korea's command economy. These were first released in 1983 in two forms, one for "socialist visitors" which had a red stamp, and one for "capitalist visitors" which had a green stamp. Another series was released in 1986 with either a blue or red Guilloché style stamp. These were issued in all denominations, except for the ₩100 note, presumably because it was assumed by the government that foreign visitors to North Korea would not show proper respect for its depiction of Kim Il-sung. These notes were discontinued in 1988 and replaced with a new series of Pakkundon in all banknote form that was more distinguishable and unmistakable from generic circulation currency.