Yoo or Yu, or sometimes Ryu or Ryoo, is the English transcription of several Korean surnames written as 유 or 류 in hangul.
As of 2000, roughly a million people are surnamed Yoo in South Korea, making up approximately 2% of the population.
The family name Yoo can be represented by any of the four hanja: 柳 (류), 劉, 兪 and 庾, each with a different meaning.
In Korean, the characters 劉 and 柳 refer to 유 (Yoo) or 류 (Ryu) and are spelled as such because of the first initial sound rule (두음 법칙) in Korean, whereas the characters 兪 and 庾 refer only to 유 (Yoo).
To avoid prosecution, the ancestor fled to Munhwa and changed his surname, first to that of his maternal grandmother, Yang, and then to Ryoo.