It is written using the hanja characters, 吳, 五, 伍, 吾, and 晤.
[1] The earliest ancestor of the Korean Oh family is believed to be Oh Eung (Korean: 오응; Hanja: 吳應) from Silla, the son of Oh Cheom known to be the Chinese royal descendant who migrated from China to Korea and married the daughter of Kim Jong-ji in Silla.
Out of these clans, the three largest clans were founded by the three brothers of Oh Hyeon-bo, Oh Hyeon-jwa, and Oh Hyun-pil, who each was given the governor position of Haeju, Dongbok, and Boseong counties as the rewards for defending Goryeo against the attack by the Khitan people.
They are regarded as being highly influential in the North Korean regime and second only to the Kim's.
[8] Most Koreans in the US prefer the surname Oh rather than O as a single letter name can often be misunderstood as an abbreviation or misprinting.