The Sutra of Accumulated Agama, in its section on Buddhas of the Future, records that Maitreya Buddha will appear in a land ruled by King GyeDu.
The land ruled by King GyeDu is called the Kingdom of Gyerim, which refers to Silla. In other words, it is present-day South Korea.
King Talhae was worried because he had no son. One morning, he heard a strange crowing sound from the forest. Upon investigation, he found a white rooster crowing beneath a golden box. Inside the box was a baby boy, whom he adopted as his son to continue the royal lineage. For this reason, the country’s name was changed to Gyerim, as recorded in Samguk Yusa.