Korea
In Korean the title was Sang-hwang (Hangul: 상황; Hanja: 上皇), or sometimes even Taesang-hwang (hangul: 태상황; hanja: 太上皇). After 1897, when the Joseon Dynasty became the dynasty of the Korean Empire, only two emperors were still to ascend to the throne. One Emperor Gojong, who was forced to abdicate by the Japanese in 1907. However, he was given the title Tae-hwangje (Hangul: 태황제; Hanja: 太皇帝). also another emperor was Emperor Sunjong. but after the Japan-Korea Annexation Treaty of 1910, the Imperial Household was demoted by the Empire of Japan.
Read more about this topic: Retired Emperor (title)