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.
Korean currency
From 1978 to 2001, the North Korean government maintained an iconic rate of 2.16 won to the US dollar; since then banks in the country exchange at rates closer to the black market rate. However, rampant inflation has been eroding the North Korean wŏn's value to such an extent that currently it is believed to be worth about the same as the South Korean wŏn (needs sourcing). In any case, the U.S. dollar and other currencies are still worth more in North Korean wŏn on the black market than officially.