Some former politicians and commanders from Anti-Japanese Revolution or Fatherland Liberation War (Korean War) have disyllabic names, one syllable for surname, one for name (김책, 강건, 최현, 남일). These names are old and this format is not used nowadays. What does this form mean?
In short, monosyllabic given names are still used, and they mostly mean not much more than their parents' preference.
These names are old and this format is not used nowadays.
No, they are not. Monosyllabic given names are less popular than disyllabic given names, but they are still considered normal and are still used. Modern (born after 1945) examples from both sides of the DMZ:
- South Korea: 강민, a former professional StarCraft player. 오혁, a rock singer-songwriter. 조권, a singer for the K-pop group 2AM.
- North Korea: 김옥, fourth wife of Kim Jong-il. 김현, an illegitimate son of Kim Il-sung. 김성, the current ambassador to the UN. 리홍, a former ambassador to Vietnam. 박철, a diplomat. 장혁, the current Minister of Railways. 최일, a table tennis player.
The use of monosyllabic names means, in most cases, nothing more than one's parents just wanted to name their children in that way.
Since Goryeo Dynasty, monosyllabic names were related to (but not restricted to) royal privilege. The founder of Joseon, born 성계(Seong-gye, 成桂) changed his name to a monosyllabic 단(Dan, 旦) after his climb to throne. His son, the second king, was born before his father's usurpation and named 방과(Bang-gwa, 芳果), but changed to 경(Gyeong, 曔) after his succession to the throne. However, his brother and successor 방원(Bang-won, 芳遠) didn't change his name.
However, this practice was not restricted to the royal family, as monosyllabic names are widely found through history: from 남이(born 1441), 권율(born 1537), to 황현(born 1855). And they are still used after the Joseon dynasty, as you gave examples yourself, and still after the partition, as you can see from the examples I gave above.
Sometimes this is a family tradition, most famously known as that of the 양천 허씨, or Yangcheon Heo Clan. They are allegedly descendants of King Suro of Geumgwan Gaya, and were known to be granted the "royal privilege of monosyllabic names" by King Taejo of Goryeo for their contribution as a vassal. Members of this clan who have used monosyllabic names span from 준(born 1539), a royal physician, to 재(born 1965), a former basketball player and manager. 허재 named his two sons 웅 and 훈, both monosyllabic.