What is "gwalleuk"

Gwalleuk was a Korean Buddhist monk from the kingdom of Baekje who lived during the time of King Wideok. In 602, he travelled to Japan and is known for helping to spread the teachings of Taoism and Buddhism to Japan. He is also said to have brought books containing knowledge of the calendar, astronomy, geography, and onmyōdō (yinyang-based teachings). He is mentioned several times in Buddhist records in Japan, where he was known as Kanroku, the Japanese reading of his name.