koreo

The person comes first. Koreo is a Korean person. The country is built from it, not the other way round: Koreio, or in the older style Koreujo. That is the ordinary Esperanto pattern for the peoples who were named before their state was, the same shape you already met in anglo and Anglio, franco and Francio, ruso and Rusio. The countries and peoples article sets out which direction each name runs in and why the two systems coexist.

North and south, stated factually. The peninsula holds two states. In Esperanto they are Nord-Koreio and Sud-Koreio, and both are also called by their own official names, Korea Popoldemokratia Respubliko and Korea Respubliko. Each government considers itself the legitimate one and neither recognises the other's claim to the whole; the language does not need to take a side, and koreo covers a person from either, because the word names the people rather than the passport.

The adjective and the language. Korea is the adjective. The language is la korea, with the noun lingvo understood - the same construction as la angla and la ĉina. A Korean woman is koreino if you need the distinction, though plain koreo is increasingly used for anyone, which the gender article discusses at length.

Esperanto in Korea. The movement there is old and unusually literary: the Korean Esperanto Association dates from 1920, and Korean was among the earlier Asian languages to get a full Esperanto textbook. It is a useful thing to know if you ever end up at a kongreso.