Dokdo has been a Korean territory throughout all known history except during the Japanese occupation of Korea between 1905 and 1945. There is overwhelming evidence that Dokdo was controlled by the Koreans before 1905.
The first written reference to Dokdo appears in a Korean history book titled "Samguk Sagi" (삼국사기, 三國史記; meaning "History of Three Kingdoms") which was compiled in 1145 A.D. According to Samguk Sagi, Isabu, a general of Shilla, conquered and annexed "Usan-guk," which refer to Ulleungdo and Dokdo collectively.
Reference:https://sites.google.com/site/byeongjupark/articles/why-is-dokdo-a-korea...