Bak Gyusu (박규수, 朴珪壽, 1807–1877) was a scholar-bureaucrat, a teacher, a politician and a diplomat of Joseon Dynasty Korea. He was known as a pioneer of the enlightenment group. Bak Gyusu was a grandson of Park Ji-won, the great Silhak scholar of the Joseon. nickname was Hwanjae (환재, 瓛齋), Hwanjae (환재, 桓齋) en Heonjae (헌재, 獻齋), Hwanjaegeosa (환재거사 瓛齋居士).
When Bak was 20, he became acquainted with Crown Prince Hyomyeong (1809-1830). They became close friends and discussed politics. When the crown prince died a sudden death, Bak was so shocked that he shut himself away for 20 years.
In 1848, He successed Gwageo exam on fourth class. In the middle of the 1870s, Pak Yeong-hyo visited Bak Gyusu and be taught about the Enlightenment Thought.Kim Okgyun was affected Bak too.
During the period of King Gojong's reign, Queen Sinjeong, who was a wife of Prince Hyomyeong, promote Bak. When the General Sherman incident occurred, Bak was the governor of Pyongan. Bak ordered the General Sherman's crew to depart from Joseon. The ship's crew ignored Bak's order and captured Yi Hyeon-ik, an adjutant of Bak. Bak rescued Yi and destroyed the General Sherman.
In 1872, Bak Gyusu was Joseon chief envoy to the court of the Tongzhi Emperor, offering congratulations.